Put every option in the config

Integrated steps per revolution and microstepping settings, also put in
travel limits for both axis
Input MS3 in config

Needs more work so that it is actually used
Integrated line numbering, checksum and resend reprap-style

Checksum code is from the Reprap wiki, if the checksum doesn't match it
requests a resend via "rs [linenumber]"
New command structure:
N[linenumber] [commands like before]*checksum