Created a dynamic library for Mac.

* The dynamic library (dylib) uses synchronous IO for now.
* Uses wchar_t for easier calling from Python.
* Has a very simple (no error checking) test program: libhashertest.c.
Added Python3 test script to load and use the library.
Added libhasher interface for Mac clients.

* Currently only exposes the HashFileWithSyncIO function.
* Uses a structure to pass data back and forth.
* Allows for a progress callback.
* Works on my machine(tm). (No testing outside my environment has been done.)