Update to 0.6.1.

Fixes #21.
Simplify initial example a bit.
Fixed: multibind, module installation.

- Multibind now works correctly with keys via MappingKey and
  SequenceKey.
- Modules can now be installed form instance, class or function, and
  injection will work correctly in all three cases.
- Added ParameterizedBuilder, which allows extra arguments to
  constructors to be declared at inject time.
Fix bug where "to" passed as a falsey value is treated as missing.
Make AssistedBuilder support CallableProvider.
0.6.2
Fix sequence key bug.
Bump to 0.6.3.
Add tracing support: injector.trace = True
Fix tracing on Python 3.
Make thread safety tests faster