Add reference serial monitor for FreeMS2 use. This is to be considered version 1.0 of the FreeMS2 serial monitor. This SM supports USB use by disabling the check on the RX pin at boot time. It is also configured as a C128 device for full normal access and no silly games during loads. This can be used on genuine MS2 and MicroSquirt devices as an upgrade for the broken SM that they ship with. Use of this SM in place of the B&G supplied SM allows use of other loading tools such as hcs12mem.