extend "load" function to work with more data types

[jeremymanning]

example here: https://github.com/ContextLab/quail/tree/loadmat
however, that code is messy, un-tested, and shouldn't be pulled into master

ideally we should support a wide variety of data formats, including everything here: http://memory.psych.upenn.edu/Data_Archive

for the writeup/release, i think we'll want to show examples from a variety of experiments to demonstrate the robustness of the toolbox

[andrewheusser]

e.g. load_example_data('murdock1962')