Updates for RC.6

[gazpachoking]

Changes to the attribute generator to support RC.6

• Separator between plugin name and key is now : rather than -
• trail and notrail modifiers renamed to trailing and notrailing
• on attribute generator no longer overloads to allow the built in 'on-x' plugins (e.g. data-on-interval). This mirrors the distinction there is now in the raw attribute names due to the change to colons as the key separator.
  i.e. data.on("interval", "expr") -> data.on_interval("expr")
• data.on_load renamed to data.init