Exposed forwardRate function.
Unit test for zero_rate and forward_rate.
Make bootstrap method return reference to term structure.
Raise NotImplementedError on calling {zero, forward}_rate when term structure is relinkable.
Fixed line breaks and indentation.
Expanded Market test case.
Fixed variable inconsistency in Market.
Get shared pointer to linked term structure for {zero, forward}_rate.
Merge pull request #53 from enthought/enh-expose-forward-rate

Expose forward_rate function on YieldTermStructure.