Pyadjoint v0.2.1

[bch0w]

Pyadjoint v0.2.1 was released this week, featuring an entire package refactor and overhaul and the addition of new misfit functions.

In addition, I brought in a number of code changes that had been incorporated by other groups (Princeton, Mines) in separate forks of the package, updated some of the internal code architecture and revamped the documentation and install procedure.

• See the full change log here: https://github.com/adjtomo/pyadjoint/blob/master/CHANGELOG.md
• Updated documentation can be found on GitHub pages: https://adjtomo.github.io/pyadjoint/
• Relevant PRs: major package refactor pyadjoint#8, Pyadjoint v0.2.0 pyadjoint#9, simplify code + polish documentation pyadjoint#10, v0.2.1 pyadjoint#11