Add Issue and PR templates

.github/ISSUE_TEMPLATE/bug_report.yml

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+# Issue template inspired by NumPy's excellent template:
+# https://github.com/numpy/numpy/edit/main/.github/ISSUE_TEMPLATE/bug-report.yml
+name: 🐞 Bug report
+description: Create a bug report to help us reproduce and fix it.
+title: "<Please write a descriptive title>"
+labels: ["bug"]
+
+body:
+  - type: markdown
+    attributes:
+      value: >-
+        Thank you for taking the time to file a bug report. First, carefully read
+        the following before everything else:
+
+          - Does your issue only arise in a library that uses Outlines? If so,
+            submit your issue to this library's issue tracker.
+          - Did you check the issue tracker for open and closed issues that may be
+            related to your bug?
+
+  - type: textarea
+    attributes:
+      label: "Describe the issue as clearly as possible:"
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: "Steps/code to reproduce the bug:"
+      description: >
+        A short code example that reproduces the problem/missing feature. It
+        should be self-contained, i.e., can be copy-pasted into the Python
+        interpreter or run as-is via `python myproblem.py`.
+      placeholder: |
+        import outlines
+
+        << your code here >>
+      render: python
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: "Expected result:"
+      description: >
+        Please describe what you expect the above example to output.
+      placeholder: |
+        << the expected result here >>
+      render: shell
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: "Error message:"
+      description: >
+        Please include the full error message, if any.
+      placeholder: |
+        << Full traceback starting from `Traceback: ...` >>
+      render: shell
+
+  - type: textarea
+    attributes:
+      label: "Outlines/Python version information:"
+      description: Please run the following code and paste the output here.
+      placeholder: |
+          import outlines; print("Outlines", outlines.__version__)
+          import sys; print("Python", sys.version)
+      render: python
+    validations:
+      required: true
+
+  - type: textarea
+    attributes:
+      label: "Context for the issue:"
+      description: |
+        Please explain how this issue affects your work or why it should be prioritized.
+      placeholder: |
+        << your explanation here >>
+    validations:
+      required: false

.github/ISSUE_TEMPLATE/config.yml

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+contact_links:
+  - name: 🤔 Questions & Help
+    url: https://github.com/outlines-dev/outlines/discussions/new
+    about: "If you have a question about how to use Outlines, please start a discussion."

.github/ISSUE_TEMPLATE/feature_request.md

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+---
+name: 🚀 New feature
+about: Request a new feature.
+title: ''
+labels: ''
+assignees: ''
+---
+
+Before suggesting a new feature, please make sure this hasn't already been suggested by searching through the past issues and the PR tracker.
+
+### Presentation of the new feature
+
+Assume that we know nothing about this feature. Please give us as much information as possible so we can judge it fairly. That includes (but is not limited to):
+- Academic article
+- Blog posts
+- Implementations
+- Personnal experience with the feature
+
+### Where does it fit in Outlines?
+
+Please explain to us why you are suggesting this feature for integration in Outlines.
+
+### Are you willing to open a PR?
+
+Tell us whether you are willing to add the feature yourself, and if so if you can share a design plan. **You may be challenged.**
+
+Thanks for contributing!

.github/ISSUE_TEMPLATE/improvement.yml

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+name: ✨ Improvement
+description: Propose an improvement to Outlines.
+title: "<Description of the proposed change>"
+labels: "enhancement"
+
+body:
+  - type: markdown
+    attributes:
+      value: >-
+        Before suggesting an improvement, please make sure this hasn't already been suggested by searching through the past issues and the PR tracker.
+
+        ## Current behavior
+
+  - type: textarea
+    attributes:
+      label: "What behavior of the library made you think about the improvement?"
+      placeholder: |
+        Sample code with the current behavior
+
+  - type: markdown
+    attributes:
+      value: >-
+        ## Desired behavior
+
+  - type: textarea
+    attributes:
+      label: "How would you like it to behave?"
+      placeholder: |
+        Sample code with the desired behavior
+
+  - type: markdown
+    attributes:
+      value: >-
+        **Be aware that your proposal may be challenged.** Outlines has strong design principles that we are committed to stick to. If there is an alternative way to achieve what you would like, we will let you know.

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

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+# 🚧 Thank you for opening a PR!
+
+A few important guidelines and requirements before we can merge your PR:
+
+- [ ] We should be able to understand what the PR does from its title only;
+- [ ] There is a high-level description of the changes;
+- [ ] *If I add a new feature*, there is an [issue][issues] discussing it already;
+- [ ] There are links to *all* the relevant issues, discussions and PRs;
+- [ ] The branch is rebased on the latest `main` commit;
+- [ ] **Commit messages** follow these [guidelines][git-guidelines];
+- [ ] One commit per logical change;
+- [ ] The code respects the current **naming conventions**;
+- [ ] Docstrings follow the [numpy style guide][docstring-guidelines];
+- [ ] `pre-commit` is installed and configured on your machine, and you ran it before opening the PR;
+- [ ] There are tests covering the changes;
+- [ ] The documentation is up-to-date;
+
+Consider opening a **Draft PR** if your work is still in progress but you would
+like some feedback from other contributors.
+
+[issues]: https://github.com/outlines-dev/outlines/issues
+[git-guidelines]: https://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html
+[docstring-guidelines]: https://numpydoc.readthedocs.io/en/latest/format.html