Allow to set IIPs for exported ports on commandline

[jonnor]

I think exported ports on top-level graph should be instantly accessible as command-line options, including generated --help docs

Embedding api should exist for this also, so once could have a "myexec" js/coffee file which just specifies graph and rest is handled by this "mounter".
This would make it very easy to make standard commandline tools using NoFlo

[ensonic]

We can add a --args key=value options that can be specified multiple times. If no graph is given on the commandline we ignore them. Otherwise:

• we create a on-the-fly component to connect tot he exports
• when it is getting loaded, we listen for "addExport" signals, for each signal emission we create ports of the opposite direction, set the IIP and connect them to the export. This might handle input parameters. If we have special values for STDIN, STDERR and STDOUT we can also stream data. If there are multiple ouput exports, only one can be selected (or we need a way to mux them).

Generating --help output is tricky is one would need to do: noflo-nodejs --help --graph abc.fbp

[jonnor]

Sounds good. That way of doing help would be acceptable for the noflo-nodejs exectuable I think