stubbed out bin function
added pointwise linear interp
started some tests
wrote some pointwise linear collapse tests
Added bins theory manual.
added monotonically decreasing functionality
Merge pull request #506 from scopatz/omcds

Pointwise Linear Group Collapse
fixed bug with monotonically decreasing versions of pointwise_linear_collapse()
cleaned up cache API
Added openmc data source, untested
Added tests for OpenMC data source
Minor missing import fix
fixed minor issue with using OpenMCDataSource for reactions that have no MT number
style updates
Merge pull request #508 from scopatz/omcds

OpenMC Data Source