Make the default __repr__ function sane.
Made the python module a proper module; and added some utility functions asvalue, asscaled and units.
Fix support for inverses where the inverse is requested as a Quantity.
Force interpretation of tuples as quantities; lists as lists of quantities.
Fixed a few bugs.
Added support for ranges and bounds.
Fix memory issue.
Add support for forward checking of bounds; and add various performance enhancements.
Bump package version.
Correct test case for constants.
Started work on cython
Use relative imports in __init__.py
Merge branch 'master' into cython
Fix cython importing.
Started using cython for speed optimisation.
Merge branch 'master' into py3

Conflicts:
	parameters/__init__.py
	parameters/definitions.pyx
	parameters/parameters.pyx
	parameters/physical_constants.py
	parameters/quantities.pyx
	parameters/units.pyx
	tests.py
Import cython code.
Fix __init__.py
Merge branch 'master' into py3
Improvements to run with python3.