Added doctest for getting group keys.
Added Travis configuration file.
Changed to install numpy/scipy with apt-get.
Removed debugging options.
Merge remote-tracking branch 'upstream/master' into placeholder

Conflicts:
	setup.cfg
Merge remote-tracking branch 'origin/fix-docs-for-field' into fix-unit-tests
Merge branch 'fix-docs-for-field' into placeholder
Merge remote-tracking branch 'origin/placeholder' into fix-unit-tests
Fixed doctest.
Fixed failing doctests. Added staticmethod.

Added
-----

* Added staticmethod decorators to methods that do not alter the grid.
  This removes the need to create an "empty" grid, which is no longer
  possible.
Changed to not squeeze corner/neighbor arrays.

Changed
-------

* Do not squeeze arrays that return corner or neighbor nodes.
Removed Python 3.x.
Fixed doctest for _make_number_of_donors_array.

Fixed
-----
* Ensure that _make_number_of_donors_array returns an array of ints.
Fixed typo. Using numpy, not np.
Fixed docstring for flow_direction.
Fixed docstring.

Fixed
-----
* Fixed failed docstring test. The parameters for flow_direction had
  changed but the doctest wasn't updated. The doctest now passes but
  still need to make sure it's doing what it is supposed to.
Fixed doctests.
Fixed doctests.

Fixed
-----
* Changed a couple of the doctests to just look at array size and type
  since the arrays are composed of random values.
Fixed doctests.
Fixed doctests.