allow `json-patch.js` and `json-patch-duplex.js` to work in browser and as Node module; add test; synchronize code changes between two versions of the library
duplex callback did not work in native Object.observe (Chrome 28+) and NodeJS; now fixed
IE8 compatibility (12 lines of code in json-patch.js; 35 in json-patch-duplex.js)
callback should contain only new patches (created after last time callback was called); make intervals configurable
jsonpatch.generate should trigger the callback in Shimmed version (it already did in Native version)
add info about testing