Ale: Add support for YAML fixer

[pbnj]

Name: yaml
URL: https://pypi.org/project/pyaml/

Neoformat can format YAML/YML files using pyaml. I would much rather use ALE for all my linter/fixer needs. ALE has support for yaml linters via swaglint or yamllint, but no yaml fixers (a much needed functionality when writing lots of yaml files by hand).

[tomsvogel]

FYI there is now prettier support for yaml.

[pbnj]

Thank you @tomsvogel .
I was not aware of that one.

Since I am already using prettier for JS, I can also use prettier for yaml. Therefore, I have no need for pyaml at this time.

[tomsvogel]

I am not 100% shure but i think to use prettier as yaml fixer ALE hast to be extended.

[pbnj]

Here is what I did and it seems to work for me:

 let g:ale_fixers      = {
    \ "*": ['trim_whitespace', 'remove_trailing_lines'],
    \ 'javascript': ['prettier', 'eslint'],
    \ 'sh': ['shfmt'],
    \ 'yaml': ['prettier'],
    \}

As long as you have prettier installed (e.g. npm i -g prettier), that should work.