Merge pull request #1 from eigenhombre/master

Add 'frequencies' function
remove identity from frequencies definition
move frequencies to recipes.py
add see also section to README
add travis.yml
turn off e-mail notifications in travis.yml
support Python 2-3 with common codebase
add dependencies section to README
Merge branch 'travis' into compat
Merge pull request #4 from mrocklin/compat

support Python 2-3 with common codebase
Add travis-ci icon