BUG: Accept int or float for bound.  Fixes failing test
updated wage parameters]
ENH: Working on vfi.

Will replace vf_iteration.py. This file may be removed.

lininterp is John Stachurski's class.  Used in value_funciton.py

attempt af vfi.  Being refactored in value_function.
Accepts an array of shocks now, but still defaults to 1.
ENH:  Add add/sub and plot methods to lininterp.