Refactor to custom exceptions & minor code style fixes

src/Exceptions/NoRecordsInvalidJSONException.php

@@ -0,0 +1,16 @@
+<?php
+
+namespace distinctm\LaravelDataSync\Exceptions;
+
+use Exception;
+use Throwable;
+
+class NoRecordsInvalidJSONException extends Exception
+{
+    public function __construct(string $message = "", int $code = 0, Throwable $previous = null)
+    {
+        parent::__construct($message, $code, $previous);
+
+        $this->message = "No records or invalid JSON for {$message} model.";
+    }
+}