Load JSON from "local" folder in browser, failover to RawGit CDN

[techmaurice]

At the moment the library loads JSON from the RawGit CDN when run in the browser. This should be "local" folders, and failover to RawGit CDN. This enables browser usage in an offline environment.

[techmaurice]

Browser now loading JSON from "local" folders.

Next up: failover for both browser and node.

[techmaurice]

This is a nice feature but not necessary, postponing it to v0.?. This feature might even never be implemented.