Add es2015 modules export, build umd with rollup and remove generated…

… code (#359)

* Remove generated code in lib and dist

Remove src out of the npm package.

* Add es2015 modules export

Remove babel-plugin-transform-runtime from the build as it is not
necessary and increases the output size for nothing.

* Use rollup instead of webpack for umd builds

Lightens the umd builds quite a bit:

    $ ll dist old
    dist:
    total 504
    -rw-r--r--  1 tusbar  staff   192K Aug 16 21:16 react-leaflet.js
    -rw-r--r--  1 tusbar  staff    50K Aug 16 21:16 react-leaflet.min.js

    old:
    total 600
    -rw-r--r--  1 tusbar  staff   263K Aug 16 21:11 react-leaflet.js
    -rw-r--r--  1 tusbar  staff    77K Aug 16 21:11 react-leaflet.min.js

* Use lodash-es for es and rollup builds

This was taken from react-redux. :)

.babelrc

@@ -1,13 +1,37 @@
 {
-  "presets": [
-    "es2015",
-    "react",
-    "stage-1"
-  ],
   "plugins": [
     "dev-expression",
     "lodash",
-    "transform-proto-to-assign",
-    "transform-runtime"
-  ]
+    "transform-proto-to-assign"
+  ],
+  "env": {
+    "development": {
+      "presets": [
+        ["es2015", { "modules": "commonjs", "loose": true }],
+        "react",
+        "stage-1"
+      ]
+    },
+    "rollup": {
+      "presets": [
+        ["es2015", { "modules": false, "loose": true }],
+        "react",
+        "stage-1"
+      ],
+      "plugins": [
+        "external-helpers",
+        "./build/use-lodash-es"
+      ]
+    },
+    "jsnext": {
+      "presets": [
+        ["es2015", { "modules": false, "loose": true }],
+        "react",
+        "stage-1"
+      ],
+      "plugins": [
+        "./build/use-lodash-es"
+      ]
+    }
+  }
 }

.gitignore

@@ -1,3 +1,7 @@
 node_modules
 bower_components
 coverage
+
+dist
+es
+lib

.npmignore

@@ -3,6 +3,7 @@ __tests__
 coverage
 docs
 example
+src
 .editorconfig
 .eslintignore
 .eslintrc.json

build/use-lodash-es.js

@@ -0,0 +1,10 @@
+module.exports = function() {
+  return {
+    visitor: {
+      ImportDeclaration(path) {
+        var source = path.node.source
+        source.value = source.value.replace(/^lodash($|\/)/, 'lodash-es$1')
+      },
+    },
+  }
+}