STM32: Moved SPI code into the common area.
Updated the documentation so that it appears in all families
Also added it to the L1 area, but is untested. An addition to the memorymap
allows commonality and a #ifdef added to the spi_common_all code to
exclude the case of SPI3 for L1 and F0 as SPI3 doesn't exist in those.
An rcc dispatch header was added to remove same code from the spi header.
Move DAC to common area
(Note there are now dummy source files dac.c (and others) that are
not compiled but are needed for documentation).
Move usart files to common area
Again added to L1 which is similar to F1
IWDG moved to common area
I2C to common area
F2/4 has now I2C3 included
CRC moved to common area
Minor cleanup to use dispatch memorymap.h
Merging pull request #72 Doc

Merge remote-tracking branch 'ksarkies/doc'

Conflicts:
	doc/stm32f1/Doxyfile
	doc/stm32f2/Doxyfile
	doc/stm32f4/Doxyfile
	lib/stm32/f1/Makefile
	lib/stm32/f2/Makefile
	lib/stm32/f4/Makefile