Problem: nvim_cmd() accepts number/boolean in args and converts them
to strings, but the keyset declares ArrayOf(String).

Solution: use ArrayOf(Union(Integer, String, Boolean)) and wrap union
types in parens when generating array annotations.

- Render Lua types in api.txt.

- Added `DictAs(name)` API type which acts the same as `Dict` (no parens)
  when generating the dispatchers, but acts the same as `Dict(name)`
  when generating docs.

- Added `Tuple(...)` API type which is the treated the as `Array` for
  generating the dispatchers, but is used to document richer types.

- Added `Enum(...)` API type to better document enums

- Improve typing of some API functions.

- Improve c_grammar to properly parse API types and replace string pattern
  logic in the parsers.

- Removed all the hardcoded type overrides in gen_eval_files.lua