Add error info to callbacks and add reject() calls

Fix #60.
Add grunt task to serve docs
Drop window.localForageConfig and add config()

Developers can now run the `config` method after localForage is
loaded rather than the weird global config from before. Fixes #135.
Add iframe test for #78
Update README to use better config (#135)
Bump version number for better config and errors

Fix #78
Handle quota exceeded error

Reject with an error in the callback/Promises rejection
on a quota exceeded error in all backends on setItem. Fix #31.
Fix dist bugs
Merge pull request #140 from mozilla/improve-errors-and-config

Improve errors and config