Mingw w64 building

Modification have been performed in order to be able to build a 64-bit Windows extension for Firefox.

Relates to issue #69.

See merge request !1

The library libgcc_s_sjlj-1.dll was missing. That was the reason why the core
libraries failed to be loaded.

When using mingw-w64 then ldns failed to build.

Configuring to build fat modules.

Removed old git-based mechanism.

Because source failed to build on Linux systems.