Support for Altium Designer Files

[sciguy14]

This pull request adds support for Altium Designer files. Altium Software is used to design printed rigid and flexible circuit boards. More info about Altium: https://www.altium.com/altium-designer/

Description

Altium uses many file types, but I've included the ones that can be represented in an ASCII format in this pull request. Many others are binary files only.

Checklist:

• I am adding a new language.
  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • .OutJob Files
      • .PcbDoc Files
      • .PrjPCB Files
      • .SchDoc Files
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s): I made the simplest possible PCB design with Altium Designer 19 and am providing the resulting sample files in this PR.
    • Sample license(s): I hereby release these sample files under a permissive license.
  • I have included a syntax highlighting grammar: https://github-lightshow.herokuapp.com/
  • I have updated the heuristics to distinguish my language from others using the same extension.

Question: It wasn't clear to me from the Contributing Guidelines - How does color selection work? I added a color to the languages.yml file, but running bundle exec rake test complained when a color was specified. The color used on all of Altium's branding is: #a5915f

[pchaigno]

Thanks for the pull request!

One quick thing to check below.

[pchaigno]

Thanks! LGTM!