* add tests for "Deno.core.encode" and "Deno.core.decode" for empty inputs
* use "Deno.core.encode" in "TextEncoder"
* use "Deno.core.decode" in "TextDecoder"
* remove "core_decode" and "core_encode" benchmarks
This commits add two new methods to "Deno.core" namespace: "encode" and "decode".
Those methods are bound in Rust to provide a) fast b) generally available of encoding and decoding UTF-8 strings.
Both methods are now used in "cli/js/dispatch_json.ts".
