Removed src/usbdevice/requests.md file
Updated Makefile.toolchain to use ARMTOOLS environment variable
Updated min/max macro definitions to specify result type
Documented XML_PARSER_BUFFERSIZE constant
Fixed documentation for AUDIO_FORMAT_TYPEI and AUDIO_FORMAT_TYPEIII
Fixed documentation warning for usb_string_descriptor_s
Implemented usb_flush to start immediate transmission (no SOF)
Added Clang property files to .gitignore