build and include promises as npm dependencies
spec update
circular references support
new System.register tests passing
circular and rebinding test completion
traceur compatibility fixes
update loaded condition check (ES bug 2602)
invariant checking
remove invariant checks
various fixes
bug commenting and fixes
correction to groupIndex algorithm
anonymous module tag support only
readme simplification
readme prep for 0.6
Merge pull request #113 from guybedford/spec-update-draft-jan-20-2014

Update to the latest spec
update package.json, bower.json
update code comments
note that Traceur runtime is optional
add simple tracing API