Reduce size of _metadata.py files

[ronaldoussoren]

The bindings for a number of frameworks, including pyobjc-framework-Cocoa have pretty large _metadata.py files. E.g., the _metadata.py for Foundation is currently 460KB and it compresses down to 56KB using gzip -9.

Find a way to optimize the size, preferably without ending up effectively obfuscating python code.

Options I've though of so far:

• Actually use compression
• Generate simpler code (calls to registerMetadataForSelector can be more compact)
• Design a binary format for the metadata and use that instead of the python code
• Compile _metadata.py into and extension module somehow (although that's likely counter productive)