Setting pulse_type for stm32 architecture doesn't do anything. Fixed this now.
fixed ezuhf file
Merge pull request #343 from gtoonstra/ppm-negative-fix

[stm32] actually honor PPM_PULSE_TYPE_NEGATIVE and trigger on falling flank
Merge pull request #344 from gtoonstra/ezuhf-config-fix

[conf] fixed ezuhf file (valid if ppm pulse_type fix for stm32 merged).
[dox] updated doxygen comments for spi interface