Transport Graphs

[WardCunningham]

This experimental version supports transporting graph-source from the equally experimental Graph plugin under development with @opn. github, comment.

A GRAPH option in the markup offers to send parsed graph data rather than waiting for a drop.

This pull request is safe to merge but unfinished. Expect improvements soon.

[WardCunningham]

I will note here a strange bug I found while debugging this.

The 'graph-source' protocol expects graph sourcing items to provide a function that returns a parsed graph. This worked fine until I added a parse function here returning the parsed transport options. The two versions of parse collided. Once I understood this, I renamed the option parser to 'options'.

This needs a better solution. A Graph should find its parse in the scope of its definition, not that of the caller. Surely there is some way to add one more layer of wrapper functions to make this so. Or maybe proper this binding, or prototypes, or ES6 classes provide the right stuff.

[WardCunningham]

I will merge and publish this and #4 as version 0.0.8.