add wakeup from touch sensor, and deep sleep example
- add new deep sleep wakeup mode
- change documentation to explain incompatibilities between different wakeup mode, add error checks
- add new ULP instructions necessary for ULP wakeup scenario
- fix issues with I_WR_REG, I_SLEEP, I_END instructions
- add deep sleep example, illustrating the use of timer, gpio, touch, and ULP wakeup triggers
See merge request !461