add functions to check if msdl is running

src/npm-data.ts

@@ -0,0 +1,16 @@
+import { exec as _exec } from 'child_process';
+import { promisify } from 'util';
+
+const exec = promisify(_exec);
+
+export async function isNpx() {
+	const output = await exec('npm list -g musescore-downloader')
+	return output.stdout.includes('(empty)');
+}
+
+export async function isLatest() {
+	const version = (/musescore-downloader@([\d\.]+)/).exec((await exec('npm list -g musescore-downloader')).stdout)![1]
+	const latest = (await exec('npm info musescore-downloader version')).stdout.trim()
+
+	return version.trim() === latest
+}