Merge pull request #2 from dogo/master

fetch master
Added new method on SCLButton that accepts a title, action block, and validation block.
Added new validation block property to SCLButton.
When the button is tapped and it has a validation block, run the block and if it fails don't continue with the button's action.
Added validation demonstration to demo app.
Fixed unintended edit.
Added validation info to README.
Merge pull request #9 from mamaral/add-validation-block

Add validation block