Split utility.py

[Holger Kohr]

The utility.py file has grown a bit beyond reasonable size, and it contains a variety of functionality that could be grouped together in a nicer way. Suggestion:

• printing.py: Stringification of stuff, including helpers for repr
• types.py: Helpers for checking/coercing (data) types
• misc.py: Everything left over

[Jonas Adler]

Agree with everything!