Preparing v0.2.2 release

[smmaurer]

This PR prepares the v0.2.2 release.

Previously merged:

• allows passing matplotlib axes to urbanaccess.plot.plot_net() (PR #68, thanks @dapid!)
• adds flexibility to calendar/date handling (PR #69, thanks @knaaptime!)
• adds user agent headers for GTFS download (PR #74, thanks to @knaaptime for bug report and initial solution)
• improves text encoding support (PR #80, thanks to @ar-kan for bug report)
• updates unit tests (PR #73)

This PR:

• updates version numbers
• updates change log
• updates versioning in docs

Release logistics:

• [x] release on pypi
• [x] release on conda-forge
• [x] update live docs
• [x] merge dev to master and tag on GitHub

Anything else to include?