Added FileSystem tracking Support.
Added file closing to the list of tracked events.
Added support for file tracking being used to track when
a file has been written to.
Added support for moving paths.
Removed specific callbacks for directories and files, opting instead
for callbacks that apply to generic paths.
Wrapped the delegate calls in exception handlers so the exceptions
would be reported, but not bubble up and be caught by the callers
of the FS methods since the callers will interpret those as problems
with the FS code and report them as such (which is very confusing).
Also removed the "willClose" call as I don't use it.
Rename FS tracking delegate did* to on* as suggested in https://github.com/kripken/emscripten/pull/1673 .
Add unit test for FS.trackingDelegate operation.
Merge pull request #2330 from juj/fs-tracking

fs-tracking