reimpl submit as field (not in separate div)
reimpl using composable fieldset, fields render functions
note: form items are now rendered in the order defined

note: the following breaking interface changes
- field() and fieldset() first parameter is now the field/fieldset name
  (which is used to identify both input elements and the container divs)

- bindInput/bindReset/bindSubmit are deprecated. Use onInput/onReset/onSubmit
  instead, passing the object method as second param, e.g. form.onInput(model, 'set')

- the generated DOM element structure is slightly different. Submit/reset/etc.
  buttons are rendered as <button> rather than <input type="submit"> for easier
  styling.

- new method form.item() gives you a low-level interface for inserting any
  structure into the form, i.e. not only those wrapped in a <div class="field">.
add form.generate() for dynamic field generation
- base field() on more generic div()
- div() binds data in update render phase to allow dynamic changes
- add subdiv() for simple container
- update examples/index.html

add preventDefault for form reset event as well as form submit
update Readme
update History; version bump