Power use is unacceptably high

[trueserve]

Right now the MCU hogs a ton of power in bootloader mode. While we don't need to be strictly low-power, the bootloader is always run at reset, and thus we want to stay as low power as possible whilst getting what we need to do done as quickly as possible. If not entering the bootloader, depending on how the application handles resets, this could be a significant power drain.

I propose:

• When not using USB, run at the best speed/performance tradeoff possible. Test power consumption before determining this speed, particularly with flash waitstates disabled
• When using USB, run the MCU at 48MHz instead of 72MHz
• Implement the LED flashing as a low speed PWM instead of the CPU-heavy loop it currently is
• Sleep whenever possible