Integrate doctest and enhanced examples

[ErikBuer]

Hi.

First off, what an amazing package you have made!

I thought i could help out with some documentation and visualization :)

Docs and Doctest

This PR adds support for doctest, that are embedded in function documentation. They are called through runtests.jl, as with the other tests. I´ve added two doc-tests as a beginning, feel free to change them to your liking. I just want a small running example.

I'd like to add doctests to more functions, as I find them as good for getting started with a library.

Seven functions were missing in the documentation, so I have added them.

Examples

I have made some small fixes to the markdown files, to clear up some markdown linter warnings.

There were some examples with code, that generated a plot.
I have implemented a setup so code examples can be written as @example that actually run when we build the docs.
This way we know that the examples work, and they generate the necessary figures while building the docs.
I have migrated example_AWGN.md so you can see a working example.

The example can now be mixture between code and text. The migrated example looks like so:

Building docs

I have made some changes to make.lj such that dependencies to run tests, and generate documentation is not included in the package itself.

I have added a CI to dry-run-build the documentation, so I was able to test the CI in my fork.
Should make things a bit easier for other contributors, being able to run the CI in their fork before creating a PR.

Now that the docs has its own dependencies, it is important to run it from the correct path, so not to add docs packages to the comms package toml.

[RGerzaguet]

Hello @ErikBuer,

Thank you so much for this comprehensive pull request. I completely agree, and the documentation changes are highly appreciated. Ensuring that the environment can be easily tested is also a necessity, and I sincerely thank you for addressing this!
Everything looks good from my end. I have reviewed the proposal, and I am now ready to merge this.
Thanks again!