Fix for node.js
Fix issue with ArrayReduction not updating PathObservers
add optional callback token
Make PathObserver.defineProperty replace its accessor with a data property of the present value when it is closed -- rather than removing the descriptor
force gc in benchmarks if possible
Added ObserveUnobserveBenchmark
remove preobserved config from Observed/Unobserved benchmark
Minor refactor: use closed flag rather than valid
cleanup on benchmark html
Merge pull request #17 from SamDuvall/master

Add node.js support
Merge pull request #19 from peterwmwong/fix-arrayreduction-path-update

Fix issue with ArrayReduction not updating PathObservers