Code and documentation string cleanup

[grlee77]

This is an attempt to follow standard PEP8 code formatting conventions and change to the numpy docstring format as discussed in #8.

No changes to functionality have been made, but a few changes were not purely stylistic:

1. replace assert statements with explicit exceptions (e.g. raise ValueError(...))
2. remove any calls to reload in the examples
3. For Python 3 compatibility, from __future__ import division, print_function, absolute_import is used throughout with // used to explicitly specify integer division where necessary.
4. Replace a few uses of numpy matrices with numpy arrays. The current recommendation of numpy developers is to avoid use of the matrix class.

I ran the current examples successfully in both Python 3.4 and Python 2.7, except for a couple I did not have data for (see #9).

Ideally, the remaining two examples should be run with proper data to make sure nothing was inadvertently broken by these changes prior to merging.

[naegelejd]

This is a bug. You're missing a comma between "grappa" and "ndarray_io".

[grlee77]

Thanks