Bond/Angle/Dihedral measure functions

[ahy3nz]

Subclasses of Connection should have a function measure() that measures that bond/angle/dihedral. This will be good for sanity-checking your simulation.

Things to consider:

• How we want to implement (define C functions like mdtraj vs just use scipy)
• Considering minimum image convention (which means the Connection instance will need to know something about the topology.box

[mattwthompson]

I think this would be a nice feature but (imo) is tangential to the core objectives and may require a good bit of work to implement in more than a primitive manner.