Merge pull request #64 from zzz0072/master

mk: remove -Wdeclaration-after-statement complie flag in mk/toolchain.mk
README: add verified version of GNU Tools for ARM Embedded
Documentation: tweak coding style slightly
make USART pin assignment configurable

Fixes #62

In preparation of new boards support other than STM32F4 Discovery, it is
necessary to make the USART pin assignment configurable. At present, both
USART4 (default) and USART2 of STM32F4DISCOVERY are supported depending on
Kconfig results.
board: bump copyright date accordingly
Avoid unexpected linker messages "Conflicting CPU architectures 13/0"

Fixes #61

The root cause of the issue is that the linker is assuming the wrong
defaults for an object which does not have a .ARM.attributes section.

We can remove all ".ARM.attributes " before linking to avoid this noise.
Please reference
http://permalink.gmane.org/gmane.comp.gnu.binutils/54317
Merge pull request #68 from georgekang/master

avoid unexpected linker message "Conflicting CPU architectures 13/0"