Soldering RT1

Some of the major updates in the firmware... (more to come)

V1.35:
- Fixed PID calculator coefficients and sampling (it could have had oscillations)
- PID tested with 12V in and duty 110-220 with low and high resistance cable, acceptable performance in all cases
- Missing to correct refresh rate of the screen (it is increased as the main loop is executed more times)

V1.4:
- Added channel tracking option in menu. Now it is possible to set one channel temperature, and both are set.

V1.5:
- Added AutoON function in menu: When changing tip, the channel goes on automatically to the set temperature.

V1.6:
- Buttons very responsive, including encoder switch
- Some code cleanup 

Software revision reached V1.3, main features:

- Programmable temperatures

- Duty cycle limitation (to use various power supply rating) programmable via menu

- Under Voltage Lock Out for lipo battery protection programmable via menu

Future implementations:

- Small updated on UVLO implementation (mostly graphical)

- Channel tracking implementation

- More ideas? :)