Release 2.1

# Release TODO List

- [x] Add a `CHANGELOG` entry summarizing meaningful changes, starting with the output of the command `git log --oneline $(git describe --tags --abbrev=0 --match "v[0-9]*" HEAD)^..`
- [x] Update vendored in libraries under `src/bin/lib`. Verify `README.md` has a reference to each library in the folder.
- [x] PG : Compare the contents of `snprintf.h , snprintf.c` and `strerror.c` in folder `src/bin/lib/pg` against PG equivalents in recent PG sources under `src/port` and apply changes to respective places.
- [x] Parson : Compare the contents of `src/bin/lib/parson` vs the source from https://github.com/kgabis/parson
- [x] ini.h: Compare `src/bin/lib/libs/ini.h` vs source at https://github.com/mattiasgustavsson/libs. Apply changes.
- [x] log.c: Compare contents of `src/bin/lib/log` vs its source from https://github.com/rxi/log.c . Apply changes as necessary
- [x] Update version number in
- [x] `src/bin/pg_autoctl/defaults.h`
- [x] `docs/conf.py`
- [x] `Makefile`
- [x] `src/bin/pg_autoctl/azure.c`
- [x] `src/monitor/metadata.h`
- [x] `src/monitor/Makefile`
- [x] `src/monitor/pgautofailover.control`
- [x] Tags should be immutable, so do **not** proceed to the next step until you're sure you have _everything_ you want in your release branch
- [x] Use `git tag -a -s v$VERSION` to create an annotated, signed tag for the release. Summarize the release in the one-line tag annotation (beneath 52 characters). Push the tag with `git push origin v$VERSION`
- [x] Visit the project's releases page (e.g. `open https://github.com/citusdata/$REPO/releases`)
- [x] Create a new release object for your git tag (i.e. `v$VERSION`). Leave the description blank (it will auto-fill with the tag description)

As for signing tags, use your own key, and ensure it's [known to GitHub](https://help.github.com/articles/adding-a-new-gpg-key-to-your-github-account/).

Closes #1005