0.5.0

This version simplifies parts of the low-level API in spirit of what was introduced in 0.4.0 to provide a more homogeneous and simpler experience.

Merged pull requests:

• Improve States: uses __dict__ so States works with vars #159 (cgarciae)
• Simplify API: Cleans-up some API details around Model and Module #158 (cgarciae)