Added new tmxr_line_attach_string API to return the attach string specific to a a particular multiplexer line.

Added parsing logic to allow tcp port and connect strings to end in either ";notelnet" or ";telnet" as desired to specifically describe a port setup.
Fixed bug in single line multiplexer attach which returned failed status when it should not have if a tcp connect destination was specified.
Relaxed parsing rules to allow a single line multiplexer to have a listen port specified at either the line level or the mux level.