MAINT set version number to 3.1.0.dev2 for a pre-release

MAINT bump version to v3.0.0

DEP get wordseg from pypi instead of a github direct link

because a github direct link as a dependency apparently doesn't
play nice with PyPI. Relevant discussions:
pypa/pip#6301
BaderLab/saber#35

MAINT bump version to 2.4.0

MAINT update repo badges in readme

MAINT update changelog

DOC add missing Sphinx static files

update readme

update readme