Minor changes to README and docs intro
Minor but significant changes to how baseline HOD constraints
are imposed on assembly biased models. All tests look good. Still need
to fold in pernicious test cases to the test suite.
Added Toy_HOD model class
Changed many mock attributes to be . No longer creating new halo table columns. Halfway through TableBundle
Finished coding up table_bundle in make_mocks. Still needs testing.

This is going to dramatically simplify development of the test suite.