release rc/2.4.0

[djkapner]

Instructions on http://confluence.corp.alleninstitute.org/pages/viewpage.action?pageId=75009306

before merge

• update version in __init__.py
• update what's new in index.rst
• update the CHANGELOG.md
• make sure github CI passes
• make sure the bamboo branch build passes.

merge!

• merge rc/x.y.z -> master

after merge

• make sure the master branch builds in bamboo
• tag the merge commit with the new version
• deploy to pypi
• deploy to production
• update the release notes on the wiki
• create a new rc branch and open a pr

[njmei]

For whoever ends up taking this on:

• Let @dougollerenshaw when 2.4.0 will be merged and released as he may need to pin the VBA analysis repository.
  For context see: major refactor of AllenSDK 2.4.0 visual_behavior_analysis#696

[djkapner]

@dougollerenshaw
responding to a comment above to alert you. I plan to merge/release this today.

[dougollerenshaw]

@djkapner thanks for the heads-up. I've pinned visual_behavior_analysis at AllenSDK 2.3.2 until we can be sure we've accounted for all of the path changes.