Broke out all functionality into plugins

packages/@zblog/toolchain/src/typings.ts

@@ -0,0 +1,9 @@
+export type MenuManifest = { name: string; link: string }[];
+export interface IPluginBuilder {
+  build(): Plugin;
+}
+
+export type Plugin = (builderContext: {
+  outputDirectory: string;
+  menuManifest: MenuManifest;
+}) => void | Promise<void>;