Initial commit - copy of druntime's core.stdc sources

This is the first of, hopefully, many pull requests to build up this library.

It is my opinion that *D-Programming-Deimos/libc* is where all C Standard Library bindings should reside for the D programming language.  Ports of *druntime* and *phobos* should link to this library instead of using `std.c` and `core.stdc`.  Hopefully, in the long-term,  the ports of *druntime* and *phobos* will gradually decouple from *libc*, and instead prefer implementations in D.

Also, as C++ interoperability matures, bindings to the C++ Standard Library should be implemented in *D-Programming-Deimos/libcpp*.

`package.json` and other files will come later.