* target.h: Add to_doc and target_preopen.

	* target.h: Add to_doc and target_preopen.
	target.c: Add target_preopen and target_command.
	Remove target_info.
	(add_target): Call add_cmd and mess with targetlist->doc.
	core.c, exec.c, remote-eb.c, remote-nindy.c, remote-vx.c,
	remote-vx.68.c, inftarg.c, remote.c: Add doc field to target struct.
	Call target_preopen from open routine.