Add arguments to serial monitor.

Calling serial monitor now requires that the user provide
the port to monitor, as well as the baud rate

Fixes #4
Fixes #5
Add basic readme.
Provide proper code highlighting markdown
Fix variables, error feedback
Re-introduce casting baud rate as an int
Merge branch 'serial-monitor-args' into serial-monitor

Conflicts:
	serial_monitor/bin/serial-monitor
	serial_monitor/lib/serial_monitor.rb