feat: language aliases

[hougesen]

Adds support for aliasing snippet languages so tools does not have to be repeated.

Closes #618 when merged.

[hougesen]

@ccoVeille I am still a bit undecided on what way the aliases should be defined.

As I see it there are 3 different options:

1

{
  "language_aliases": {
    "language": "is_alias_of"
  }
}

2

{
  "language_aliases": {
    "is_alias_of": "language"
  }
}

3

{
  "language_aliases": {
    "is_alias_of": ["language1", "language2"]
  }
}

Which way do you think makes most sense?