Add explicit import for
Fix compilation of Then, when the first action returns a value
Allow nullable locations

Change `Location` to be a `Maybe (Expression ())` to support compilation of
programs where only the side effect is interesting.
Merge pull request #118 from Feldspar/maybeloc

Maybe location
Cleanup
Add testcase for nullable locations
Update the bindToThen test case
Add missing case in encodeType
Remove unused import
Cleanup
Fix typo.