Remove extra whitespace
Tidy up some runtime things

* Rename stream -> evented-property
* Reorganise a little bit.
Lots of refactoring:

* Separate hooks/expressions/helpers
* Add registerHelper, registerExpression
* Rename stream to property/event
* Add the javascript builtin operators as expressions
    - (*,+,-,/,%,<,>,==,===,leq, geq) (leq and geq instead of <= and >=
      as the html parser breaks on <=)