Merge pull request #1 from qrilka/master

Small fix for sample
Added `callWithErrorHandling` which supports a failure handler
Merge pull request #2 from ajnsit/master

Added `callWithErrorHandling` which supports a failure handler
Always overwrite files
Minor Fay API change
Missing json is a user error
Version bump
Require fay 0.11
fay 0.12
Fixes to make yesod-fay and sample work with Fay 0.13