Uses cython only if present.

[alexis-mignon]

Check whether cython is installed or not. If so, comilation is performed from the .pyx file, otherwise from the .c file.

[coveralls]

Coverage remained the same at 100.0% when pulling 8e48103 on alexis-mignon:setup_with_cython into 74a389b on dedupeio:master.

[coveralls]

Coverage remained the same at 100.0% when pulling d65403a on alexis-mignon:setup_with_cython into 74a389b on dedupeio:master.

[alexis-mignon]

Looks like there are problems with the continuous integration:

• The upgrade of pip fails in Travis
• The include dir for stdint does not seem to be added in appveyor.

[alexis-mignon]

• Looks like the NumpyExtension class does not have the same behaviour in python 2 and 3. For python 2 case, when used with cython, it leaded to compat/win32 not being added to include dirs.

• The error in travis is due do pip not being installed when compiling for osX, or maybe pip2 or pip3 should be used instead of pip: OSX: pip command not found travis-ci/travis-ci#8829

[fgregg]

thanks! merged your changes in another branch