Added a lsusb utility script

`lsusb` is a Linux command that lists all devices currently
attached to the USB bus. Mac OS X doesn't have this command, but
provides the `system_profiler SPUSBDataType` utility. This formula
installsa script that emulates Linux's lsusb behaviour, while
providing similar functionality and syntax.

This version has been tested in Mac OS X 10.6-9, and should work
in any Mac system that provides the `system_profiler` command.
Added man page

Added documentation for the lsusb command