update doc to reflect view and formField methods
Relax testing presence of value attribute a bit

When the value field is added via props in an ampersand-view (e.g.
ampersand-input-view), the hasOwnProperty test does not succeed. This
allows additionally the value to be a getter that returns a truthy
value.
Merge pull request #4 from whobubble/master

update doc to reflect view and formField methods