[example] Example how to use the LSP client

To run

```bash
$ cd test/server
$ npx tsc -b . && node src/simple_client.js
```

test/server/src/simple_client.ts

@@ -0,0 +1,42 @@
+import * as Protocol from "vscode-languageserver-protocol";
+import * as Types from "vscode-languageserver-types";
+import * as LS from "./LanguageServer"; 
+
+async function start() {
+  let languageServer = LS.start();
+  let initializeParameters: Partial<Protocol.InitializeParams> = {
+    rootPath: ".",
+    rootUri: ".",
+    trace: "verbose",
+    workspaceFolders: null,
+  };
+  let result = await languageServer.initialize(initializeParameters);
+  return languageServer;
+}
+
+async function sendSimpleDoc(languageServer : LS.LanguageServer, text : string) {
+    let textDocument = Types.TextDocumentItem.create(
+        "file.v",
+        "coq",
+        0,
+        text,
+      );
+    await languageServer.sendNotification(
+      Protocol.DidOpenTextDocumentNotification.type,
+        {
+          textDocument,
+        },
+      );
+}
+function printDiags(params : Protocol.PublishDiagnosticsParams) {
+    console.log(`${params.diagnostics.length} diagnostics received`);
+    console.log(params.diagnostics);
+}
+
+start().then((ls) => {
+    console.log("Starting");
+    ls.onNotification(Protocol.PublishDiagnosticsNotification.type, printDiags);
+    sendSimpleDoc(ls, "Definition a := 3. Variable (b : nat). Error. ").then(() => {
+        setTimeout(() => { ls.exit(); }, 5000)
+    })
+});