alias dir for consistency in the website

maybe move all web dirs in misc.py to usui?
Merge branch 'master' into rename-dir-path
Merge branch 'master' into rename-dir-path
saving default ytransform as '' instead of null
Function for mapping column names to the tables that contain them.
Function for registering table merges as broadcasts of one onto the other.
merge_tables function for merging tables according to broadcasts.
Merge pull request #65 from synthicity/mergetables

Function for merging tables according to registered broadcasts
not changing the default ytransform
Merge pull request #71 from synthicity/rename-dir-path

Rename dir path for configs_dir to models_dir
Merge branch 'master' into new-simulation-testing

Conflicts:
	urbansim/sim/simulation.py