Enum for languages

[pnewstein]

Currently, setting the language for posts and comments is difficult, because you need to know the integer that corresponds to the language ID.

This pull request adds an Enum for the language IDs. So now you can do:

from pythorhead.types import LanguageType
# Get lemmy object, login
lemmy.post.create(community_id, "title", language_id=LanguageType.EN)

Using an int is still supported

lemmy.post.create(community_id, "title", language_id=37)