Small fixes in naming and comments
Added Oja's rule
Added unit test for oja's rule
Simplified oja's rule and renamed to voja's rule
Created Dict Network for adaptive (key, value) associations
Added unit tests for Dict Network
Small tweaks to Voja's docstring
Improved documentation and made voja test more strict
Merge branch 'learning_oja' of https://github.com/ctn-waterloo/nengo into learning_oja

Conflicts:
	nengo/builder.py
	nengo/networks/data_structures.py
	nengo/objects.py
	nengo/tests/test_connection.py