Move all generators-related code to their own module
Move the content of "common" to the root of the module
Remove indentation system from generators
Move `write_enum` implementation to the `generators` module root
Move write_type_aliases into module root
Add gl_generator/target to .gitignore
Fix all bugs introduced in the current PR
Merge pull request #171 from tomaka/cleanup

Clean up implementation (step 1)