Support system dsc_extractor.bundle

• Prefer the default dsc_extractor.bundle installed at /usr/lib/dsc_extractor.bundle if you don't have Xcode installed
• Allow passing a custom dsc_extractor.bundle path as a 4th argument if you want to prefer that (or any other library) over the one discovered in Xcode

Thanks @Alkenso!

Rewrite in C

0.2.0

Replace with C (#2)

Initial release

0.1.0

Update installation instructions