Most changes are noise from doxygen.
Readme udpated to explain newer FP_FLAGS for m7
stm32f7 library is skipped if the toolchain doesn't support it yet.
Renamed every instance of variable CFLAGS in target specific Makefiles
to TGT_CFLAGS to free up CFLAGS for user defined compiler flags.
Added information in README.md about existence and usage of CFLAGS
environment variable in build process.
