Rewrite of Giallo internals

Rewrite of Giallo internals, the code should be clearer about intention,
flow. Also enable cover, fix dialyzer
Add doc target and some minor doc cleanups
Merge pull request #13 from bipthelin/bt-fixes

Rewrite of Giallo internals
Minor fix, send in Req instead of Env to before_/2
Merge pull request #14 from bipthelin/bt-fixes

Minor fix, send in Req instead of Env to before_/2
Only check to see if init/3 exist
Merge pull request #15 from bipthelin/bt-fixes

Only check to see if init/3 exist
Prepare to tag 0.1.0