New: c.kak ; Modified: cpp.kak

Commit messages:
~~~
Add semicolon after union in cpp.kak ; created new c.kak and moved C associations to c.kak from cpp.kak
~~~

Comments:
I had to do all my modifications blind this time since I don't understand much of kak's syntax yet, so please review before merging >^,^<

New file c.kak:
* I don't understand much of kak's syntax yet, so I copied cpp.kak to c.kak and edited it blindly.
* I removed most CPP-only features (from c.kak, not from cpp.kak)
* I added several C-only features (such as _Atomic, _Bool, etc)
* I tried to change the regex to support stdint.h types but I didn't test it yet.
* I added filetype associations for C (.c,.h,x-c).
* I tried to change any hooks, etc, with "cpp" in the name or pattern to the same but with "c" instead of "cpp"
* In c.kak, BUT NOT cpp.kak, I commented out two features that didn't seem to be working in cpp.kak

Changes in cpp.kak:
* You had code that (according to a comment) would add a semicolon after class|struct blocks.  I extended this to union blocks.
* I removed most filetype associations for C (.c,.h,x-c) while leaving the CPP associations alone (.cpp,...,x-c++).

C++ unions do need a semicolon too, right?  I'm strictly a C programmer so this was really just a guess.