build: install generated mongoc-config.h
build: add libmongoc-ssl-1.0.pc

This allows consumers to check for the presence of libmongoc, but require
SSL support. The libraries are in fact the same, but libmongoc-ssl-1.0
will only be present if the library was compiled with SSL support.

If using autoconf, you can check with:

  PKG_CHECK_MODULES(MONGOC, [libmongoc-ssl-1.0])

Fixes CDRIVER-260.