Added workaround to get Python 3.7 on Travis.

Updated changelog and version numbers for 4.1.0 release.

Updated changelog and version numbers for 4.0.3 release.

Updated changelog and version numbers for new 4.0.2 release.

Changed documentation link to point to RTD, since pythonhosted is goi…

…ng away. Added python_requires setup argument.

Updated changelog and set version number to 4.0.0 for release.

Updated changelog and set version number to 3.0.0.

Updated changelog and set version to 2.3.2 for new release.

Updated changelog and set version to 2.3.1 for new release.

Updated changelog and set version to 2.3.0 for new release.