Added test function at the package level to run all tests.
Remove spurious prints in testing.
Changed value of testing to remove 1/0 warning.
Changed testing infrastructure to use BaseTestCase to check for unwanted warnings
Return None in functions that modify quantities in place

- Quantity.ito
- Quantity.ito_base_units

See:

https://docs.python.org/3.3/tutorial/datastructures.html#id3

BACKWARDS INCOMPATIBLE CHANGE
Quantity unit conversion methods are now independent from their in-place relatives.

Previously, `Quantity.to` was calling `Quantity.ito` after a copy operation. In the
same way, `Quantity.to_base_units` was calling `Quantity.ito_base_units`. Now, each
function has it's independent code path which call the right math (in-place or not
in-place) function.
Allow assigning Not a Number to a quantity array.

Close #127
Fix in setitem
Fix bug where conversion would fail b/c of caching

Return copies from from_string lru_cache
Merge branch 'jdreaver-master' into develop
Added a standard way to change the registry used in unpickling operations.

Close #148
Change internal function run_pyroma to _run_pyroma
Added docstring and return value in test functions.
Fixed typos in comments and docs
Merge branch 'master' of git://github.com/infraredgirl/pint into develop
Removed incorrect text from the tutorial

Close #149
Fixed download links in documentation

Download links for ePub and zipped HTML were switched around.
Merge branch 'fix_links' of git://github.com/infraredgirl/pint into develop
Updated the contributing section of the docs
Updated CHANGES