Revert "const char*" arguments to their original const-qualified

Revert "const char*" arguments to their original const-qualified
	types, now that I have modified the typemap to support this.
Add "opaquechar" and "struct datachunk" types, used to get binary data
	strings in and out of C respectively.
These are used by ZOOM_connection_option_setl() and
	ZOOM_connection_option_getl() respectively.
Implemented ZOOM_connection_error_x().
Tested ZOOM_connection_{errcode,errmsg,addinfo)().
Tested ZOOM_options_create().
Add explicit "UNTESTED" markers to not-yet-tested functions.