Add cacheing of tables, columns, and injectables.
Switch simulation tests to use setup/teardown funcs.
Make sure fake_data_home is cleaned up after tests.
Remove old file and add pmat.py to .coveragerc.
Reset caches when replacing things in the registry

Includes: tables, columns, and injectables.
Merge pull request #80 from synthicity/sim-cache

Add cacheing in simulations