find_signal: find blocks with a named input or output signal

A wrapper for find_system which selects blocks with a named input or output signal.

A limitation of find_system is that you can't search for blocks by specifying just one of their input or output signal names. You can search for blocks with a specific set of input or output names by using the InputSignalNames and OutputSignalNames parameters, but only exact matches are returned.
This function allows you to specify just one input or output signal name, and every block which has an input or output signal with that name is returned, regardless of how many other inputs or outputs it has.

The matching is case sensitive, and this version does not support regular expressions.

The syntax is similar to that of find_system, and includes the same options for extending or limiting the scope of the search. Examples and help are included in the file.