Abbreviated numpy namespace

All modules now use:
    import numpy as np
Abbreviated masked array namespace

All modules now use:
    import numpy.ma as ma
Numpy namespace abbreviations in documentation
Numpy namespace abbreviations in test code
human readable datetimes and cube unit printout
Merge pull request #338 from ajdawson/numpy-namespace

Standardising numpy namespaces
Merge pull request #323 from cpelley/print_units

Improved str() support: Cube units, and human-readable dates.
nimrod orog loading + line lengths
mockography
proper nimrod rules and unit test