Remove support for old-old rcjk lib format

[justvanrossum]

• Remove support for old-old rcjk lib format
• Use fallbacks for missing rcjk lib keys
• Avoid some code duplication by setting lib variable to self._RGlyph.lib

This fixes #35.

[justvanrossum]

I am uncertain about the traceback printing in the except part. I needed it to debug the try part, but perhaps it is a common case for new glyphs?

[justvanrossum]

Although: if this was meant to catch KeyErrors, then the try/except is no longer needed at all: all three lib keys now have fallbacks.

[justvanrossum]

Yes, I think it's better to completely remove the try/except.