Added release notes and bumped version to 1.13.1 (#1170)

* Added release notes for 1.13.1

* Bump version to 1.13.1 for release.

Bump version: 1.12.1-dev → 1.13.0 (#1156)

Added release notes for 1.12.0 (#1112)

* Added release notes for 1.13.0

* version error

* bumped version to 1.12

* fix for removal of errant release notes line

Merge pull request #1091 from robfalck/rel_notes_1_11_0

Added release notes for 1.11.0

Added release notes and version bump for dymos 1.10.0 (#1022)

* added release notes for dymos 1.10.0

* bump version to 1.10.0

* Fixed release notes mention of vanderpol update.

Release notes for 1.9.1 (#995)

* Release notes for 1.9.1

* bump version to 1.9.1

Added release notes for 1.9.0 (#983)

* added release notes for 1.9.0

* bump version to 1.9.0

Bump version 1.8.0 (#924)

* bump version to release 1.8.0

Added release notes and version bump for 1.7.0 (#901)

* Added release notes for 1.7.0
* Bump version: 1.6.2-dev → 1.7.0-dev
* Bump version: 1.7.0-dev → 1.7.0

Release notes for 1.6.1 (#860)

* added release notes for 1.6.1

* bump version --> 1.6.1