Fast Base64 decode for embedding binary in JSON files

In the visual effects world base64 is often embedded in text-based scene formats to optimize loading speed and space.

Here is a fast Base64 encoder/decoder that outperforms the built-in JSON.parse routine for an array of floats by more than 30%, see here:

http://jsperf.com/json-vs-base64

For an array of arbitrary floats, base64 is also 3 times more compact in terms of characters used. 

The combination of speed and space savings can be significant if this is adopted as an alternative to just straight JSON.stringify-ing arrays of floats.