WIP: Deprecate std.c.* and move all remaining declarations to core.stdc.*

I'm still working on this, thought I'd get the first cut of the low-hanging fruit up on the auto-tester before I move forward with the more involved modules.  Ultimately, it will need to be merged simultaneously as [druntime pull #893](https://github.com/D-Programming-Language/druntime/pull/893).

I used the same process to deprecate `std.c.string` recently.  If anybody sees any problems with the pull so far, please speak up.
Add `core.sys.windows.stdlib` and declare `setenv` and `unsetenv` in it would be better, because it is consistent with `core.sys.posix.stdlib`