New pie wedgeEventsEnable/Disable implementations

- The wedgeEventsEnable and wedgeEventsDisable methods now increment and
  decrement a counter.  When the counter is 0, mouse events are enabled,
  otherwise they are disabled.  As a result, multiple calls to
  wedgeEventsDisable require a matching number of calls to
  wedgeEventsEnable to turn wedge mouse events back on.  This is useful if
  multiple animations will happen in succession and the goal is to
  disable mouse througouth the entire transaction.
- Simplified generateId method in core.
Merge pull request #11 from gsmith85/promise-fix-and-mouse-in-path-fix

New pie wedgeEventsEnable/Disable implementations
allowing tooltip container to dynamically size.  Tooltip containers are
specified by css class .elroi-tooltip-container.  Changed for line as
well as stacked bar graphs.
Merge pull request #12 from ahahn/tooltip-container-dynamic-sizing

allowing tooltip container to dynamically size.
Adds missing $document variable

- The $document variable should have been included with commit
  681fd0f.  Without it getRelativeMousePosition generates errors.