Doc fix: clearify that alias prop setter returns True to cause dispatch.
Copy observers list when dispatching to prevent observers from being eaten.
Add rebind option to Property to allow dynamic rebinding of properties in kv.
Implement dynamic rebinding of properties in .kv for properties that enable it.
Move rebind from Property to only those that implement it. Add docs.
Add nosetests for property rebind.
Move func def out of func for better performance.
Some optimizations.
Merge branch 'master' of https://github.com/kivy/kivy into rebind2
Merge pull request #2174 from matham/rebind2

Introduces rebind keyword for some properties to enable dynamic rebinding