Add libclinic.clanguage module and move the following classes and
functions there:
* CLanguage
* declare_parser()
Add libclinic.codegen and move the following classes there:
* BlockPrinter
* BufferSeries
* Destination
Move the following functions to libclinic.function:
* permute_left_option_groups()
* permute_optional_groups()
* permute_right_option_groups()