Bump version and update CHANGELOG

Also use https links in sidebar in docs

See CHANGELOG for details

Bump version -> 0.8.4

Update changelog and version 0.8.2 -> 0.8.3

Bump version 0.8.1 -> 0.8.2

Bump version

Bump version -> 0.8.0

Suppress scikit-learn warning

This is fine, since TextBlob doesn't support Scikitlearn classifiers
Also, bump version to 0.7.1

Bump version 0.7.0-dev -> 0.7.0

Bumpversion 0.6.3-alpha -> 0.6.3