fix(ngRepeat): handle iteration over identical obj values

Modifies default trackByIdFn to factor both key and value into hashKey
for non-array primitive (i.e. index not provided) values

Closes #2787
Closes #2806
fix(form): pick the right attribute name for ngForm

Closes #2997
feat(ngRepeat): add $even and $odd props to iterator
fix(ngMobile): prevent ngClick when item disabled

 - the ngClick attribute was always triggered, regardless the ngDisabled/disabled attributes
 - we now check the DOM disabled status before triggering the original click event

Closes #3124
Closes #3132
fix(select): don't support binding to select[multiple]

changing the type of select box from single to multiple or the other way around
at runtime is currently not supported and the two-way binding does odd stuff
when such situation happens.

we might eventually support this, but for now we are just going to not allow
binding to select[multiple] to prevent people from relying on something that
doesn't work.

BREAKING CHANGE: binding to select[multiple] directly or via ngMultiple (ng-multiple)
directive is not supported. This feature never worked with two-way data-binding,
so it's not expected that anybody actually depends on it.

Closes #3230
fix(ngMobile): emit click event for touchy clicks

Previously, no handlers for the click event would be called for the
fast, touch-based ngMobile clicks, only for desktop browser clicks. Now
the event will fire properly for all clicks.

Closes #3219
Closes #3218
Closes #3137
chore(ngdocs): replace showdown.js with marked.js