Added doctest for getting group keys.
Added documentation.

Added
-----
* Added lots of new examplesand doctests.
* Fomatted for numpydoc.

Changed
-------
* Methods that take ids as arguments should be able to accept a scalar,
  array-like, or nothing to indicate a single id, a set of ids, or all
  ids, respectively. Going through and updating this where possible.
Changed decorators to use functools.wraps.
Added more documentation and doctests.
Changed unit_test to _unit_test.
Updated rst files with sphinx-apidoc.
Minor doc tweaks

Light editing on tutorial.rst and radiation_field.rst
Added Travis configuration file.
Changed to install numpy/scipy with apt-get.
Removed debugging options.
Merge pull request #34 from mcflugen/fix-raster-docs

Update RasterModelGrid docs
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 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.