Prepare release 0.21 (#176)

* Update documentation

* Bump 0.21 version

* Fix doc

* Update notebook

Prepare release 0.20.0 (#170)

Prepare release 0.19.0 (#160)

* Bump version to 0.19.0

* Update changelog

Prepare release 0.18.1 (#151)

* Update CHANGELOG

* Bump 0.18.1

Prepare release 0.18 (#149)

* Bump 0.18

* Relax test tolerance to pass on macosx

Bump version 0.17 (#147)

Prepare release 0.16 (#142)

* Update changelog

* Bump version to 0.16

Prepare release 0.15.3 (#139)

Prepare release 0.15.2 (#137)

* Lint README

* Bump 0.15.2

* Fix moe smooth derivatives test and some cleanup

Bump 0.15.1