conda forge fix for Windows

Merge pull request #65 from alexlib/npy_isnan

_isnan is replaced by np.isnan

conda installation package

after replacing _isnan by np.isnan we hope to get through the conda forge test for windows

preparation for conda-forge

updated continuous integration and test on Travis-CI
updated list of contributors
preparation towards conda-forge

0.20.1

fixes the bug in the Cython library for 32-bit and 64-bit Windows platforms