Add a Disabled constructor to allow programmatic disabling of forms
Merge remote-tracking branch 'mightybyte/master' into disabled

Conflicts:
	digestive-functors-heist/digestive-functors-heist.cabal
Implement Disabled constuctor using Metadata
Modify df-heist to work with the new viewDisabled
Generalize formSplice and make it subsume formSplice' in the process
Accept heist 0.12
Bump lower bound
Merge remote-tracking branch 'soostone/master'

Conflicts:
	digestive-functors-heist/digestive-functors-heist.cabal
	digestive-functors-heist/src/Text/Digestive/Heist.hs
	digestive-functors/src/Text/Digestive/Form.hs
	digestive-functors/src/Text/Digestive/Form/Internal.hs
	digestive-functors/src/Text/Digestive/View.hs