Remove '\n' from charset when not in DOTALL mode.

Fixes #4
Support categories (like '\w') in regular expressions.

Fixes #3
Update docs now that DOTALL isn't assumed.
Complain loudly on unsupported flags, with bug links.
Support capping the number of repeats.
Merge branch 'categories'

This adds support for basic categories, sufficient to close
https://code.google.com/p/sre-yield/issues/detail?id=3
Merge branch 'dotall'

Conflicts:
	test_sre_yield.py

Sufficient to close
https://code.google.com/p/sre-yield/issues/detail?id=4
Merge branch 'error-flags'
Merge branch 'repeat-limit'

Conflicts:
	sre_yield.py
	test_sre_yield.py

Sufficient for closing
https://code.google.com/p/sre-yield/issues/detail?id=1
as the tests now pass on both test machines.