Include stdint.h for uint8_t

Some compilers will be unable to compile this file without stdint.h.
Check for stdint.h in mkmf config

Just in case some "weird" non-C99 platform that we support doesn't have
a stdint.h header but it has all the others, let's make sure we don't
blindly try to include the file if it's not there.
doc: Add Abhinav Gupta to the AUTHORS section
Merge branch 'abhinav/patch-1' into next

* abhinav/patch-1:
  doc: Add Abhinav Gupta to the AUTHORS section
  Check for stdint.h in mkmf config
  Include stdint.h for uint8_t