Add xasm language.

[pfusik]

I add the language "xasm".

Description

It is the assembly language of the 6502 CPU with some extensions. See https://github.com/pfusik/xasm

Checklist:

• I am associating a language with a new file extension.

  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am adding a new language.

  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    I expect it is used in dozens, not hundreds of GitHub repositories
    • Search results for each extension:
      I was unable to create a query for the whole GitHub, so here it is narrowed to my user:
      • https://github.com/search?q=user%3Apfusik+extension%3Aasx
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • I wrote hello.asx myself
    • Sample license(s): WTFPL
  • I have included a syntax highlighting grammar.
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am fixing a misclassified language

  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am changing the source of a syntax highlighting grammar

  • Old: https://github-lightshow.herokuapp.com/
  • New: https://github-lightshow.herokuapp.com/

• I am adding new or changing current functionality

  • I have added or updated the tests for the new or changed functionality.

[pchaigno]

We prefer sample files from "real applications" under permissive licenses. Hello worlds and very short programs are usually not a good fit since we use those files to train the Bayesian classifier.

[pchaigno]

Thanks for the pull request @pfusik!

I expect it is used in dozens, not hundreds of GitHub repositories

That's a requirement unfortunately. I'll tag the pull request as pending popularity and we can revisit when there are hundreds of repositories.

[pfusik]

I see, thanks!

[pchaigno]

Closing in favor of #4219. We'll monitor the popularity of the extension there.

If you have an improved search query compared to the one used in #4219, please post it here and I'll update #4219.