Release 2.1.0 prep

Summary:
Prepping for `2.1.0`

- [x] Bump version numbers
- [x] Rebase this branch after remaining PRs are closed
- [ ] Run `pod install` (**must be done internally**)
- [x] Re-gen docs
Closes Instagram#380

Reviewed By: rnystrom

Differential Revision: D4381222

Pulled By: jessesquires

fbshipit-source-id: 04646168d3c84d0dd2c08f0a357836b9326f8963

Update CHANGELOG.md

Summary: Closes Instagram#311

Differential Revision: D4307618

Pulled By: jessesquires

fbshipit-source-id: 0698436fdeeec9c6d4a776376572025e6e8e6ee4

Pod file updates

Summary: Pod files were skipped after API renames.

Reviewed By: jessesquires

Differential Revision: D4003106

fbshipit-source-id: d3b5336a8e98880549d4414d679cbeff94169a01