BUG: Clean up unit parser context.
BUG: Add S for Siemens.
ENH: Special-case all weird labels so all units can be round-tripped through the parser.
ENH: Make the parser handle offsets.
Merge branch 'master' into fix/clean-unit-parser-context

* master:
  BUG: Fix the definition for PPG.
  turn off the deprecated API
  provide (PyArrayObject*) casting for arrays passed to PyArray_DATA
  pyArray_DOUBLE -> NPY_DOUBLE
  NPY_IN_ARRAY -> NPY_ARRAY_IN_ARRAY; NPY_INOUT_ARRAY -> NPY_ARRAY_INOUT_ARRAY

Conflicts:
	scimath/units/tests/units_test_case.py
ENH: Document CHANGES.
Merge pull request #25 from enthought/fix/clean-unit-parser-context

BUG: Clean up unit parser context.