Fix #7.

This is done via a new module Data.Singletons.Exports that contains
all the exported names for singletons. The singleton generation can
then use the TH quoting syntax to pull real names, instead of using
the dirty mkName. This also means that there are orphan instances,
but that's OK.
Turn on warning checking in "Quickly"; remove badPlus feature.

In the initial version of singletons, including code in a promotion
block that was missing a type signature was a warning. This is silly;
it should be an error. This is now fixed.
Fix "Star" test case.
Remove dead code. No more dependency on syb!
Remove `promoteDataCon` in favor of `PromotedT`. Addresses js/#22.