Added test package in nix flake to automatically run tests.

To be able to do such, it was required to add the vendor directory
to the git project.

vendor/denopkg.com/chiefbiiko/std-encoding@v1.1.1/mod.ts

@@ -0,0 +1,56 @@
+import * as base64 from "https://deno.land/x/base64@v0.2.1/mod.ts";
+import * as base64url from "https://deno.land/x/base64@v0.2.1/base64url.ts";
+
+const decoder: TextDecoder = new TextDecoder();
+const encoder: TextEncoder = new TextEncoder();
+
+/** Serializes a Uint8Array to a hexadecimal string. */
+function toHexString(buf: Uint8Array): string {
+  return buf.reduce(
+    (hex: string, byte: number): string =>
+      `${hex}${byte < 16 ? "0" : ""}${byte.toString(16)}`,
+    "",
+  );
+}
+
+/** Deserializes a Uint8Array from a hexadecimal string. */
+function fromHexString(hex: string): Uint8Array {
+  const len: number = hex.length;
+  if (len % 2 || !/^[0-9a-fA-F]+$/.test(hex)) {
+    throw new TypeError("Invalid hex string.");
+  }
+  hex = hex.toLowerCase();
+  const buf: Uint8Array = new Uint8Array(Math.floor(len / 2));
+  const end: number = len / 2;
+  for (let i: number = 0; i < end; ++i) {
+    buf[i] = parseInt(hex.substr(i * 2, 2), 16);
+  }
+  return buf;
+}
+
+/** Decodes a Uint8Array to utf8-, base64-, or hex-encoded string. */
+export function decode(buf: Uint8Array, encoding: string = "utf8"): string {
+  if (/^utf-?8$/i.test(encoding)) {
+    return decoder.decode(buf);
+  } else if (/^base64$/i.test(encoding)) {
+    return base64.fromUint8Array(buf);
+  } else if (/^base64url$/i.test(encoding)) {
+    return base64url.fromUint8Array(buf);
+  } else if (/^hex(?:adecimal)?$/i.test(encoding)) {
+    return toHexString(buf);
+  } else {
+    throw new TypeError("Unsupported string encoding.");
+  }
+}
+
+export function encode(str: string, encoding: string = "utf8"): Uint8Array {
+  if (/^utf-?8$/i.test(encoding)) {
+    return encoder.encode(str);
+  } else if (/^base64(?:url)?$/i.test(encoding)) {
+    return base64.toUint8Array(str);
+  } else if (/^hex(?:adecimal)?$/i.test(encoding)) {
+    return fromHexString(str);
+  } else {
+    throw new TypeError("Unsupported string encoding.");
+  }
+}