Performance improvements and a new feature

This version introduces many performance improvements throughout the runtime library and the feature to decode unsigned integers into signed Go integers when this is accurate. This feature makes the library more compatible with other MessagePack implementations (most of which by default encode non-negative integers as unsigned integers).

0.9.1

Various improvements, refactoring

Stable, but planning more features and improvements

0.9.0

Added fix to ignore blank identifier aliased imports