Performance gains for hex and base64

[jawj]

Following up on #364, I created a new package — hextreme — for fast hex and base64 encoding and decoding, and I've updated this library to use it.

The tests are passing, and I've added benchmarks that show performance gains (in Node) of 3 – 13x:

Before:

BrowserBuffer#toString("hex") x 72,483 ops/sec ±0.19% (99 runs sampled) NodeBuffer#toString("hex") x 527,266 ops/sec ±0.33% (97 runs sampled) Fastest is NodeBuffer#toString("hex") BrowserBuffer#from(hexString, "hex") x 54,803 ops/sec ±0.84% (95 runs sampled) NodeBuffer#from(hexString, "hex") x 342,656 ops/sec ±0.14% (97 runs sampled) Fastest is NodeBuffer#from(hexString, "hex") BrowserBuffer#toString("base64") x 30,815 ops/sec ±0.18% (94 runs sampled) NodeBuffer#toString("base64") x 2,594,667 ops/sec ±0.44% (97 runs sampled) Fastest is NodeBuffer#toString("base64") BrowserBuffer#from(base64String, "base64") x 28,184 ops/sec ±0.36% (97 runs sampled) NodeBuffer#from(base64String, "base64") x 1,218,393 ops/sec ±0.40% (96 runs sampled) Fastest is NodeBuffer#from(base64String, "base64") 

After:

BrowserBuffer#toString("hex") x 348,151 ops/sec ±0.51% (97 runs sampled) NodeBuffer#toString("hex") x 545,605 ops/sec ±0.60% (96 runs sampled) Fastest is NodeBuffer#toString("hex") BrowserBuffer#from(hexString, "hex") x 187,737 ops/sec ±0.29% (95 runs sampled) NodeBuffer#from(hexString, "hex") x 348,078 ops/sec ±0.24% (98 runs sampled) Fastest is NodeBuffer#from(hexString, "hex") BrowserBuffer#toString("base64") x 404,447 ops/sec ±0.27% (98 runs sampled) NodeBuffer#toString("base64") x 2,658,187 ops/sec ±0.42% (97 runs sampled) Fastest is NodeBuffer#toString("base64") BrowserBuffer#from(base64String, "base64") x 92,365 ops/sec ±0.45% (98 runs sampled) NodeBuffer#from(base64String, "base64") x 1,167,713 ops/sec ±1.30% (92 runs sampled) Fastest is NodeBuffer#from(base64String, "base64") 

Please let me know if you need anything else in order to be able to merge this.

[jawj]

This change should also make it very easy to add support for base64url (#314) since hextreme supports that.

[dcousens]

A new dependency as non-battle-tested as a newly published package - unfortunately - isn't tenable for Buffer.

The TextDecoder option presented previously was an easy option as the complexity of review remained in band.

[jawj]

OK. Kind of disappointing, but I guess I see where you're coming from. I'll start again and probably just do toString('hex') for now.