feat(BEAM): Add support for Erlang, Elixir, and Gleam comments

[kikofernandez]

Adds support for comments for the most used BEAM languages:

• Erlang

• Elixir

• Gleam

• Added a change log entry in changelog.d/<directory>/.

• Added self to copyright blurb of touched files.

• Added self to AUTHORS.rst.

• My changes do not contradict
  the current specification.

• I agree to license my contribution under the licenses indicated in the
  changed files.

[kikofernandez]

Thanks @maennchen for reminding me of Erlang's lexer and parser generators, which are now included in the PR :)

[floriansnow]

This looks identical to PythonCommentStyle. Do you see any differences or do you think they styles will diverge in the future?

[kikofernandez]

I do not see any differences, but I thought that maybe one does not want to conflate comment styles for different languages, in case in a few years one comment style changes a bit, while the other should not.

Happy to be wrong and I can fix to use Python style, if you think this is more maintainable 😃

[floriansnow]

I mean I'm just getting back into the codebase, but from what I can see, many languages use the same code style definition and it wouldn't be an issue to add another one should they diverge in the future.

[kikofernandez]

Ok, can you confirm that I understand that the preference is to follow PythonCommentStyle?
Just to confirm that I understood correctly that I should modify this

[floriansnow]

Yes, that's what I prefer, but let's wait with changes until we have the confirmation that I'm not just missing something.

[floriansnow]

I think CppCommentStyle will serve the same purpose here, won't it?

[kikofernandez]

I am not sure it would work, as Gleam does not have multiline as CPP

-- copy-pasted CppCommentStyle snippet
MULTI_LINE = MultiLineSegments("/*", "*", "*/")

and the CppCommentStyle also uses some php SHEBANG which I do not think work on Gleam

-- copy-pasted CppCommentStyle snippet
SHEBANGS = [
        "#!",  #  V-Lang
        "<?php",  # PHP
    ]

[floriansnow]

If I'm not completely off, using CppCommentStyle would only cause a problem if there was a chance for something that looks like a multiline comment in Gleam, but isn't one. The same should also be true for the shebang. @carmenbianca can you confirm?

[kikofernandez]

To be honest, I do not think it is an issue in Gleam, but I have not written much Gleam myself.
I mention this as to separate concerns :)
Please let me know what the preferred way would be :)