Yara yls support

[TcM1911]

This adds Yara support to ALE using Avast's language server for yara:
https://avast.github.io/yls/

A .git folder is used to determine the project_root so this means the
Yara rules must be in a git repo for the integration to work.

The server only have 1 optional argument (-v, --verbose). Since this is
the case, no additional configuration options are available.

[hsanson]

Please add an entry for the new linter in doc/ale-supported-languages-and-tools.txt file and this is missing a callback function to handle the linter output.

[TcM1911]

@hsanson, I've added an entry to doc/ale-supported-languages-and-tools.txt. With regards to the "missing callback" function, I don't know what you are referring to. I'm not seeing any references to it in the dev doc. I used Zig zls as a template for this implementation. So with regards to tests, the yls linter tests are essentially testing the same as the linter tests for zls.