Added impliedVolatility to DividendVanillaOption
Conforming method names and arguments to PEP8.  Added tests for dividend_american_option and implied volatility method.

Eliminated unnecessary digit in dividend_american_option_implied_volatility test.
Editing travis.yml - got rid of cython_0.16 patch.
Merge pull request #27 from dstephens99/travis-test

This pull request includes my previous pull request, plus removing the cython_0.16 patch from travis.yml