Improve error handling and code structure

src/errors.ts

@@ -0,0 +1,12 @@
+
+export class SyncIDNotFoundError extends Error {
+    readonly fileID: string;
+
+    constructor(fileID: string) {
+        super(`SyncID not found for file ${fileID}`);
+        this.fileID = fileID;
+        Object.setPrototypeOf(this, new.target.prototype);
+    }
+}
+
+export class UnchangedProtyleError extends Error {}