Add multiple build targets, for umd and es5. (#1)

* Add multiple build targets, for umd, es5 and es6.

* Remove lodash.camelcase.

rollup.config.ts

@@ -0,0 +1,34 @@
+// Based upon https://github.com/alexjoverm/typescript-library-starter/blob/master/rollup.config.ts
+
+import commonjs from 'rollup-plugin-commonjs';
+import resolve from 'rollup-plugin-node-resolve';
+import sourceMaps from 'rollup-plugin-sourcemaps';
+
+const pkg = require('./package.json');
+
+const libraryName = 'index';
+
+export default {
+  input: `dist/es/${libraryName}.js`,
+  output: [
+    { file: pkg.main, name: libraryName, format: 'umd' },
+    { file: pkg.module, format: 'es' },
+  ],
+  sourcemap: true,
+  // Indicate here external modules you don't wanna include in your bundle (i.e.: 'lodash')
+  external: [],
+  watch: {
+    include: 'dist/es/**',
+  },
+  plugins: [
+    // Allow bundling cjs modules (unlike webpack, rollup doesn't understand cjs)
+    commonjs(),
+    // Allow node_modules resolution, so you can use 'external' to control
+    // which external modules to include in the bundle
+    // https://github.com/rollup/rollup-plugin-node-resolve#usage
+    resolve(),
+
+    // Resolve source maps to the original source
+    sourceMaps(),
+  ],
+};