The Read String routine reads a string from a virtual keyboard.

    Format

      SMG$READ_STRING  keyboard-id ,resultant-string [,prompt-string]

                       [,maximum-length] [,modifiers] [,timeout]

                       [,terminator-set] [,resultant-length]

                       [,word-terminator-code] [,display-id]

                       [,initial-string] [,rendition-set]

                       [,rendition-complement] [,terminator-string]