added Tooltip class and removed d3.tip dependancy.  Adding some tests
added unit tests for util helper functions and some tests for drawing of tooltip
Merge pull request #78 from tpkelly/master

Refactor initialisers
merged tom's refactor
fixed conflict in zip file
added a helper function and some comments
removed d3 tip js file and lib folder
fixed bug in test that didn't work on travis
Merge pull request #79 from Stavrakakis/master

Removing d3-tip dependency