Minor cleanup experiment.py
Tabs to 4 spaces in threshold
Add assertions to curvefit.fitWLC()
Adding threshold.py with StateFinder and unittests
browser.ExperimentBrowser refactored; includes with_directory() method
Fix directory kwarg in browser.byMolecule()
Added meanStiffness() to TrapData; import constants
Fix misspelled function in Pulling.fitForceExtension()
Adding multiple region curve fitting for MMS rips
Clean curvefit.MS_rip_region()
Renaming test data files to standard conventions
Adding fitWLCrip() testing
Fit.plot() only shows fit to data it was fit to

Instead of generating the fit for all the x data available, it uses
the self.fitOutput variable which was generated  when fitting.

This is to prevent errors when plotting MMS_rip_region() fits which
are not 1-1 function over force.
Fixed bug in TrapData.maskFromLimits() which created mask with size n-1 from actual data
Fixed curvefit.MMS_rip_region() to use append correctly for n>1 rips

Also moved fitWLC_masks to top
Add Pulling.fitRegions() for multiple rip fitting