add lorentzian function
TST : fix travis to actually use current head
correction on functions
add tests
change api file
TST : give up on using conda recipe for now

 - travis makes a shallow clone of the target repo
 - conda-build tries to make a clone of the shallow clone which fails
Merge pull request #150 from tacaswell/travis_conda_fix

Travis conda fix
clean up
change doc
rm rst file
Merge pull request #149 from licode/more_function

ENH : More functions to be used in fitting