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.
I've been moving the contents of these `std.c.*` modules to druntime in the accompanying pull, so it's to be expected that they don't pass the tester alone.  Dan Murphy will test both pulls together in his autotester before committing, as he did for the earlier deprecation of `std.c.string`.