Much overdue commit, swiftly moving towards v1.0

* Basic example documentation
* Exception handling for non-positive LENGTH and STRIDE
* More sensible but still arbitrary defaults for LENGTH and STRIDE
* Removed un-used class attributes from Goldilocks
* Prevented additional appending of underscore to raw sequences during
  repeated calling of the Goldilocks census
* Allow non-integer chromosome identifiers
* Fixed serious bug with group_counts for total track
* Allow y-axis limits to be applied to all plots
* Allow results for multiple chromosomes to be placed on the same plot
* Improved axis labels on plots
* Functionality to save plots to file
* New regression test to ensure sorting by min is successful