Bin rewrite

The reason the testserver command did not work (as posted in issue https://github.com/alexfernandez/loadtest/issues/2) is that windows handles the command line parameters differently to unix systems. 
i asked @izs if there's the possibility to do a generic reference in the package.json file (https://twitter.com/zaphod1984/status/373380501060341760) but that is not possible.

i added two files to the bin folder, changed the reference in package.json and did a rewrite for the command line parsing (introducing the command line parsing module `optimist`).

hope you like it.