Merge pull request #5 from geraintpalmer/master

Added three tests for every method, except got a strange error when tryi...
Merge pull request #6 from geraintpalmer/master

starting work on cum_transition_row method
Have a doctest for cumulative row sum
refactored have event method to release
Added a lot of error handling (could do this forever)
Have methods that could/should replace sorting
Have removed all sorts
Jason's fix for the insert method