Consistent Cell-Cell ordering, and seperate Cell-scalar semantics.
Tweak docstring and comments
Merge pull request #311 from rhattersley/cell-comparison

Consistent Cell-Cell ordering, and seperate Cell-scalar semantics.
Merge remote branch 'upstream/v1.1.x'

* upstream/v1.1.x:
  Tweak docstring and comments
  Consistent Cell-Cell ordering, and seperate Cell-scalar semantics.
unit conversion on assignment.
Mod to allow arithmetic operations on comaptible units. Also updated
docs.
Honouring ctype parameter for converting arrays of integers
Modifications following initial feedback. Move to methods rather than
properties for conversion.
Added entry to CHANGES.
Fixes to docstrings.