Added datapoint merging
Initial implementation of overlap routine
Finished initial gain re-refinement and normalisation.

Added test suite which contains normalisation tests for variance, value
and metadata.
Split out calibrations, finished background subtraction and tests
Added tests of vertical shift, fixed small bug
Improved metadata storage and testing coverage. Added a cache for
efficiency files to improve speed.
Converted reduction metadata to use CifFile; fixed regain calculation

All metadata provided by the reduction process is now stored in a CifFile
object within the Dataset. An error in gain variance calculation was fixed
and gain recalculation metadata added.
Split calibrations into separate file and added output format choice
Added and tested the Ford and Rollett gain correction, improved testing framework.