Add initial minecraft-java-manager scaffold

Initial project scaffold for minecraft-java-manager. Adds package.json and package-lock.json, README update, index.js entrypoint and test.js. Introduces src modules: checker (detects Java version), installer (downloads JRE components with redirects, SHA1 validation, progress/events and concurrency), web (fetches launcher/runtime manifests and component data), systeminfo (platform key and install path resolution) and config (endpoints). Declares dependencies adm-zip and node-downloader-helper.

src/web.js

@@ -0,0 +1,40 @@
+const config = require("./config")
+
+async function getVersionManifest(version) {
+    const mainifestRequest = await fetch(config.launcherManifest.get())
+    const manifest = await mainifestRequest.json()
+    const component = manifest.versions.find($version => $version.id == version)
+    if (!typeof component == "object") {
+        throw new Error("Unknown version")
+    }
+    return component.url
+}
+
+async function getRequiredJREFor(versionUrl) {
+    const mainifestRequest = await fetch(versionUrl)
+    const manifest = await mainifestRequest.json()
+    return manifest.javaVersion
+}
+
+async function getJREComponentDetails(componentRequested, os) {
+    const mainifestRequest = await fetch(config.allRuntimes.get())
+    const manifest = await mainifestRequest.json()
+    const component = manifest[os][componentRequested]
+    if (typeof component != "object") {
+        throw new Error("No JRE Component found")
+    }
+    return component
+}
+
+async function getJREComponentManifest(url) {
+    const mainifestRequest = await fetch(url)
+    const manifest = await mainifestRequest.json()
+    return manifest
+}
+
+module.exports = {
+    getVersionManifest,
+    getRequiredJREFor,
+    getJREComponentDetails,
+    getJREComponentManifest
+}