stm32f4discovery long-term deep sleep

[southernbear]

Use deep sleep to save power consumption.

• Enter Stop Mode when long-term sleeping(more than 1s) and wake up by RTC.
• Provide automatic RTC calibration synchronized with TIM2.

[OlegHahm]

@haukepetersen, could look at this?

[ghost]

Merged build triggered.

[ghost]

Merged build started.

[ghost]

Merged build finished.

[haukepetersen]

1. I dont quite understand the coupling of the RTC with TIM2, especially the part with searching for the nearest channel of TIM2
2. The code formatting is not quite RIOT-style (way to many empty lines)
3. Comments missing (page headers, doxygen) and some comments in the code could help

[thomaseichinger]

@southernbear @haukepetersen
Regarding the future closing of this repository is this PR anyhow maintained?

[haukepetersen]

Not sure - as I would be very interested in the functionality and it should be of course moved into the main repo as soon as the questions above are solved.

[ghost]

Can anyone ask me to verify this patch?

[miri64]

@RIOT-OS-Jenkins test this please