add SER_ERR_NOT_OPEN status code
add SER_BAUD_56_875
add serial driver for Atari, still contains much debug code
remove debug code
remove old (static) serial driver boilerplate
small optimzation (found by Greg King)
Merge pull request #64 from groessler/something_to_pull

Serial driver for Atari
Merge remote-tracking branch 'upstream/master'

Conflicts:
	libsrc/atari/ser/atrrdev.s