Added notes on how the abstracts are represented, ensured all the class
hierarchies were up to date, and changed the orientation so the classes
are actually readable in the big chart.
Add Servo and AngularServo implementation along with docs and tests.
This is a deliberately minimal implementation designed to be added to as
we agree on new extensions (better than making an all-singing,
all-dancing version in which I get things wrong and then wind up making
backward incompatible changes to get it right :)
The prototypes in the docs are rigged to make out the first parameter as
mandatory (as it effectively is); however this does mean you've got to
remember to update the prototype when you modify it in the code! :)
