Add support for std::vector<double> and std::vector<int> in swig wrappers
Remove units before calling wrapped functions.

This allows the passing of numpy arrays, as these
are converted to lists before calling.
Added %apply statements for OUTPUT parameters.

The pythhon swig wrappers now return output parameters as a tuple.
Added units to output
Updated swig wrappers.

Wrappers now include:
- Support for STL vectors.
- Automatic removal of units
- Automatic conversion of numpy arrays to lists
- Addition of units to output parameters
- Proper handling of OUTPUT reference parameters
Restructured test
Replaced with stripUnits with one from simtk.openmm
Add missing import of simtk.unit
Merge pull request #9 from jlmaccal/master

Updated swig wrappers.
Merge branch 'upstream'

Conflicts:
	python/exampleplugin.i
Use stripUnits from main openmm public interface.
We do not support double precision.

We currently do not properly support double precision. So,
we now throw an exception when the context has useDoublePrecision
set. We no longer test double precision as part of `make test`.
Added tests for DistanceRestraints.
Added tests for selection by groups and collections.
Switched to assert macro to compare vectors.
Merge branch 'master' of https://github.com/maccallumlab/meld-openmm-plugin
Merge branch 'master' of https://github.com/grollins/meld-openmm-plugin

it.