Recent debian testing and ubuntu 15.10 releases contain a
gcc-arm-none-eabi toolchain that returns 0 for the test with -mcpu and
-fsyntax-only, despite not actually supporting cortex-m7. They then
failed hard on actual compilation steps.
Use the --help=target output instead. tested with old g-a-e 4.7 and
newer releases.
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.
