Add preliminary support for STM32F0 branch Cortex-M0

Supported modules:

MEMORYMAP (partially tested)
IRQ (untested)
RCC
GPIO
FLASH (untested)
PWR (untested)
M0 core (partially tested)

TODO for later update:
* Some common files from cm0 and cm3 are same and needs to be grouped.
* GPIO is same as in F24, common gpio file needs to be renamed to gpio_common_f024 (undone due
to merge this change with F3 compatibility in one commit - f0234 ). GPIO is NOT compatible with F1 !!

Style may be correct, i was repeatedly check this commit many times before pull request.