modifications and add-ons

adds mapping so input is from -100 to 100. Allows for linking and
unlinking of motors. Working with potentiometer. Maps 0-1023 analog
input to -127 to 127. Untested in water
updates and bug fixes

remapped manual to full stop to full ahead. Fixed e-stop fighting with
manual. Fixed linking bug while in manual.
Merge pull request #6 from spsuauv04/master

Ready for maker faire