Defer loading of wasm file

[fregante]

If you use the import() function the website will be usable earlier (e.g. it can start resolving the graph) while it downloads this huge dependency.

docs/graphvizlib.d416b260.wasm      ⚠️  1 MB
docs/index.80c6c8bb.js                  368.92 KB   

[broofa]

Good point.

FWIW, this was the most problematic part of switching to Parcel. I ended up removing d3-graphviz because it relied on @hpcc/wasm's default behavior for loading the WASM file, which wasn't working with parcel bundling. Not a big surprise that, I suppose. Switching to import() shouldn't be a big deal as long as parcel groks what's going on there.