Added support for testing with travis
Changes UnitRegistry to use instance variables.

This changes `_UNITS`, `_PREFIXES` and `_SUFFIXES`
to behave as expected.

Fixes hgrecco/pint#9.
Merge pull request #10 from bwanders/master

Multiple UnitRegistry instances without interference
Fix #7 -- always use real division.
Merge pull request #12 from dbrnz/real_division

Fix #7 -- always use real division.
Merged master
Initial work to support non multiplicative units
Refactoring of the codebase

The pint module was split into different modules within the pint package.
The refactoring aims to provide better ways to test and extend pint.
In particular, it tries to separate code that does not require knowledge
of the registry. It also crete new classes to simplify the Quantity class.
Fixes and cleanups to the unit module

- Fixed future imports.
- Fixed parser to accept dimensions surrounded by square brackets.
- Added pi_theorem as a function from UnitRegistry
- Added value convert function to the UnitRegistry
- Added some documentation
Fixed NumPy tests to support comparison of Quantities and arrays
Implemented transformation of NumPy array content for ufunc call
Added future imports
Added "in" as an abbreviation for "inches"
Added "lightyear" as synonym for "light-year"
Added MPH
Added kph
Add support for more ufuncs and improved testings.
Added support for more NumPy funcs

- All NumPy test pass in Python 2.7.
- Bitwise related test removed.
Moved tests inside package
Improved naming of methods and added docs