Rename Protocol to IO, move all commands to Command
Add an explicit data type for protocol
Adjust configure file

Protocol_sexp --> IO_sexp
Fix short_types_01 test after parser changes
Reset command: return a dummy position for compatibility
Add more type annotation to Protocol
Misc.find_in_path: always return canonical filename
protocol: Add typing information for completion command
Merge branch 'type-protocol' into experimental

Conflicts:
	src/command.ml