Option to display only the shortest path(s) between two nodes

[waldyrious]

(Related to #5)

This functionality could certainly help clean up the graph, as well as make the tool more potentially useful in practice.

For example: https://akr.am/languages/?source=C&target=JavaScript displays the shortest path

C --[Clang]--> LLVM --[Emscripten]--> JavaScript

but also a few others that take more convoluted routes. It would be nice to be able to turn those off.