oslinfo --param lets you print info on just one parameter.

Also switch oslinfo to use ArgParse.

Example output:

    $ oslinfo test
    shader "test"
    float s  0
    float t  0
    float foo  1
    float bar  13
    output color outputColor  [ 0 1 0 ]

    $ oslinfo --param foo test
    shader "test"
    float foo  1