Move tests and sample data to test/
Update README.org

Specify master branch for Travis badge
Consolidate test statements
Add function to filter data structure

Only works on flat structures right now.  This should be used and
let-bound to a variable when that variable is going to be used a lot.
Theoretically, it should be faster than traversing through the entire
data structure.  Think of this as a Emacs-local version of the API's own
filter.
Add sample data for development testing
Merge branch 'convenience-functions' of github.com:vermiculus/stack-mode into convenience-functions
More work on data filter; add tests