Work on https://github.com/neovim/neovim/issues/459

This lint job will ensure that the C codebase is properly formatted at
all times. This helps eliminate most of clint.py.

To save CI time, it's faster to manually compile uncrustify and cache
the binary instead of using homebrew (the apt-get package is too old).

Work on https://github.com/neovim/neovim/issues/459

This warning is essentially only triggered for ported vim functions.
It's unlikely that we'll refactor vim functions solely based on their
size since it'd mean we'd greatly deviate from vim, which is a high cost
when it comes to importing the vim patches. Thus, this warning only
serves as an annoyance and should be removed.

Problem:    K_SPECIAL may be escaped twice.
Solution:   Avoid double escaping. (closes vim/vim#10340)
https://github.com/vim/vim/commit/db08887f24d20be11d184ce321bc0890613e42bd

Add space around arithmetic operators '+' and '-'.
Remove space between back-to-back parentheses, i.e. ')(' vs. ') ('.
Remove space between '((' or '))' of control statements.
Add space between ')' and '{' of control statements.
Remove space between function name and '(' on function declaration.
Collapse empty blocks between '{' and '}'.
Remove newline at the end of the file.
Remove newline between 'enum' and '{'.
Remove newline between '}' and ')' in a function invocation.
Remove newline between '}' and 'while' of 'do' statement.

Problem:    Using \{xxx} for encoding a modifier is not nice.
Solution:   Use \<*xxx> instead, since it's the same as \<xxx> but producing a
            different code.
https://github.com/vim/vim/commit/fccd93f0917234b962ce07d1df3adf9d7105936f

Use this notation in langmap_spec.

Problem:    GUI tests fail because the test doesn't use a modifier.
Solution:   Add "\{xxx}" to be able to encode a modifier.
https://github.com/vim/vim/commit/ebe9d34aa07037cff2188a8dd424ee1f59cbb0bf

Change macros to enums to use them in unit tests.

Problem:    Cannot map <C-H> when modifyOtherKeys is enabled.
Solution:   Add the <C-H> mapping twice, both with modifier and as 0x08.  Use
            only the first one when modifyOtherKeys has been detected.
https://github.com/vim/vim/commit/459fd785e4a8d044147a3f83a5fca8748528aa84

Add REPTERM_NO_SPECIAL instead of REPTERM_SPECIAL because the meaning of
"special" is different between Vim and Nvim.
Omit seenModifyOtherKeys as Nvim supports attaching multiple UIs.
Omit tests as they send terminal codes.
Keep the behavior of API functions.