Provide callback parameter

Required to use asynchronous tasks.
Explicitly import fs
Added optional callback testReady(test).

The testReady(test) is called before a test function is run with
the same test object that will be handed to the test function.
This allows for decorating the test object with additional
functionality.

For instance, in the case of
http://github.com/dalnefre/tart-nodeunit it enables adding
test.sponsor(...) and test.dispatch(...) without changing nodeunit.
NPM installation instruction updated.
Merge pull request #237 from prometheansacrifice/master

NPM installation instruction updated.
Merge pull request #233 from robacarp/tap_reporter_updates

Tap reporter updates
Merge pull request #235 from tristanls/test-ready

Added optional callback testReady(test).
merged