implemented a lot of features

lib/yenc/errors.ts

@@ -0,0 +1,16 @@
+export class YencError extends Error {
+  constructor(message: string) {
+    super(message)
+    this.name = 'YencError'
+  }
+}
+
+export class YencCrcError extends YencError {
+  constructor(
+    public readonly expected: string,
+    public readonly actual: string
+  ) {
+    super(`CRC32 mismatch: expected ${expected}, got ${actual}`)
+    this.name = 'YencCrcError'
+  }
+}