GitLab

* Added FAQ links to error messages

* Added missing Windows export

Refactored ForceImpl, lots of KernelImpl subclasses, and other related classes to avoid redundant calculations when requesting a State with both forces and energies

Redesigned CustomNonbondedForce to eliminate combining rules and allow the expression to directly use parameters for individual particles.

Changed how kernels get initialized.  StandardMMForceField now has you set the 1-4 interactions explicitly.  CMMotionRemover allows the removal frequency to be set.

Modified the initialization order of ForceImpls to prevent them from trying to initialize themselves before the Platform had been chosen

Created a test case for StandardMMForceFieldImpl's findExclusions() method.  Fixed some bugs that it found.  Created a CMake script and configured it for building and running test cases.