Release 2.12.1 (pyscf#3106)

* Release 2.12.1

Release 2.12.0 (pyscf#3087)

* Release 2.12.0

* Update CHANGELOG

Release 2.11 (pyscf#2991)

* Release 2.11

* Update Contributors list

Release 2.10 (pyscf#2889)

* Update FEATURES file

* Release 2.10

* Update changelog

* Update changelog

* Update developers list

Release 2.9 (pyscf#2765)

Release 2.8

Release 2.7 (pyscf#2407)

* Release 2.7

Patch release 2.6.2

Patch release 2.6.1

Release 2.6