GitLab

* Created OBC2 that works with current force fields

* Created HCT, OBC1, GBn, and GBn2 that works with current force fields

* Added documentation for GB models

* Updates to documentation and tests based on comments

* Added formula for screening parameter

* Top level Python module is now "openmm"

* Updated module names in examples

* Updated module names in documentation

* Updated module in CI scripts

* Added deprecation warning

* Made ordering of impropers more deterministic

* Fixed typo

* Do not alter mass of hydrogens in rigid water

* Do not alter mass of hydrogens in rigid water