Release version 0.4.0

Compatible with NxSDK 0.7.0

Added

• Added version tracking to documentation.

Changed

• An error is now raised if a learning rule is applied to a non-decoded connection. (#103)
• Switched documentation to new nengo-sphinx-theme. (#143)

Fixed

• Snips directory included when pip installing nengo-loihi. (#134)
• Closing nengo_loihi.Simulator will now close all the inner sub-simulators as well. (#102)