wkranec/finance — pull request #30 by tubedude (2014-05-08 20:38:39+00:00)
Title: Added optional Guess rate to IRR and XIRR

For some Cashflows I was getting ```RuntimeError: Singular Jacobian matrix. No change at x[0]```. To avoid that I've added an optional param to IRR and XIRR methods to accept a Guess Rate.
The default is ```f.one``` but now you can add a number as a starting point of the calculations.