Reorganized existing examples, and started on some simple new examples.
Started on the most basic parallel tempering example possible.
So far, the current interface is looking like a pain in the ass.
This also doesn't run---still debugging why.
Added import of HamiltonianExchange, ParallelTempering, and ReplicaExchange into repex module import so we can use idiom "from repex import ParallelTempering".
Added fix and test for #79
Minor fix
Merge pull request #84 from choderalab/robin

[WIP] Added fix and test for #79 (Round Robin coordinate selection)
Added some ugly hacks to get around the fact that MCMCSamplerState needs to create a Context to initialize the sampler state with energies and correct velocities/positions.
Changed 'platform' from a parameter dict key/value pair (which could never be stored in the database) to an optional argument to all of the myriad constructors.
Lots of bugfixes all over for platform handling.
Example now uses only vacuum simulation because GBSA CPU implementations segfaults on my platform.
Added another missing reference to platform in execution of hard-coded Langevin dynamics move set.
Fixed issue with example script.
Fixed some more issues where platform information was not being correctly used on resuming.
Fixed another case in ParallelTempering where platform information was not being used.
Found yet another constructor for ReplicaExchange that I had missed before.  Added platform awareness.
Drastic simplification/speedup to parallel tempering energy calculation.
Split alanine dipeptide parallel tempering example into implicit and explicit solvent versions.
Attempting to add pressure to explicit solvent example, but example is failing with error.
Various bugfixes and barostat checking fix.
Merge pull request #1 from jchodera/pressure

Various bugfixes and barostat checking fix.
Added single test with pressure.
Merge pull request #2 from jchodera/addtest

Added single test with pressure.