Tx, mbridge, add support for requesting an option by index

[olliw42]

for lua scripts on memory constraint systems we may need to be able to request the settings for a parameter individually. See #74.

[olliw42]

I have added support for calling a parameter by index. 0bd0aad
In the latest commit is also find an example lua script where this mechanism is used instead of the RequestList approach. It should help to realize how the byIndex mechanism is used.

hopefully this helps with getting better along with a bw script

@jasonwang01 FYI