Fixed some basic formatting errors in the combinatorics functions.
Set up run_one function to return separate correlator pieces
Modified correlators to do light-light disconnected diagram
Updated tests to reflect changes in correlators.
Forced data import to discard imaginary part of correlators.
Added function containing measurements for fitting of excited states
Added missing scipy optimize import
Removed additional system path for pyQCD import
Fixed several bugs in fitting measurements and used existing single state fitting functions in pyQCD
Added measurements module to docs