piecemeal 0.3.0

Basic data structures your 2D game may need.

0.3.0

• Get rid of implicit casts and dynamic.
• Make Rng.item() and Rng.take() generic methods.
• Add Rng.float().

0.2.1

• Make strong mode clean.
• Fix bug in Rect.clamp().

0.2.0

• Make constants lowerCamelCase.
• Remove sign() and clamp() since the Dart core libraries have them now.

0.1.1

• CARDINAL and INTERCARDINAL direction lists to Direction.