feat(#99): introduce spot REST client

examples/rest-spot-public.ts

@@ -0,0 +1,18 @@
+import { SpotClient } from '../src/index';
+
+// or
+// import { SpotClient } from 'bybit-api';
+
+const client = new SpotClient();
+
+const symbol = 'BTCUSDT';
+
+(async () => {
+  try {
+    // console.log('getSymbols: ', await client.getSymbols());
+    // console.log('getOrderBook: ', await client.getOrderBook(symbol));
+    console.log('getOrderBook: ', await client.getOrderBook(symbol));
+  } catch (e) {
+    console.error('request failed: ', e);
+  }
+})();