New: Invalidation and data set methods.

- New API methods:
  - rows().invalidate() - Invalidate the matched rows
  - row().invalidate() - Invalidate the matched row
  - row().data( set ) - Set the data to use for the matched row

- This involves building upon the invalidation work done in the last few
  commits and creating an invalidation function. This new function will
  mark the cached data as invalid for re-reading by the sort and
  filtering methods (this will need to be abstracted into modules in
  1.11, but there is no infrastructure for that yet - that's what 1.11
  is all about). Additionally the invalidation method will update either
  the data held by DataTables (read from the DOM), or update the DOM if
  the data source was not the DOM. A flag allows an override to state
  the direction, although I think that generally speaking you might not
  want to use the override (you might nuke parts of your data source
  object if you read from the dom for example).