feat: export header and Babel preset (#5)

These two things are almost identical across our projects already and it
makes a lot of sense to have them shared from a single source.

Babel preset (TypeScript and CSS are optional):
```json
{
  "exclude": ["**/node_modules/**"],
  "presets": [["vis-dev-utils/babel-preset", { "css": true, "ts": true }]]
}
```

Header (reads package.json):
```javascript
import { generateHeader } from "vis-dev-utils";

const banner = generateHeader();
```

custom values can be supplied if necessary (tsdoc included):
```javascript
const banner = generateHeader({ name: 'vis-timeline and vis-graph2d' });
```

.babelrc

@@ -1,17 +1,4 @@
 {
-  "presets": [
-    [
-      "@babel/preset-env",
-      {
-        "targets": "maintained node versions",
-        "useBuiltIns": "usage",
-        "corejs": 3
-      }
-    ],
-    "@babel/preset-typescript"
-  ],
-  "plugins": [
-    "@babel/proposal-class-properties",
-    "@babel/proposal-object-rest-spread"
-  ]
+  "exclude": ["**/node_modules/**"],
+  "presets": [["./babel-preset", { "ts": true }]]
 }

.eslintignore

@@ -1,3 +1,5 @@
 !/.eslintrc
 /bin
+/declarations
 /dist
+/lib

.gitignore

@@ -20,5 +20,7 @@
 
 # built files
 /bin
+/declarations
 /dist
-/vis-dev-util-0.0.0-no-version.tgz
+/lib
+/vis-dev-utils-0.0.0-no-version.tgz

babel-preset/index.js

@@ -0,0 +1,75 @@
+module.exports = function(_context, { css = false, ts = false } = {}) {
+  const base = {
+    presets: [
+      [
+        require("@babel/preset-env"),
+        {
+          targets: {
+            // A browser is polyfilled if it is supported by it's maintainers
+            // or if it is used by at least one in every thousand of users.
+            browsers: "> 0.1% or not dead",
+            // This forces Babel to polyfill ESM as if it was UMD. The reason
+            // behind this is that that Babel doesn't include IE 11 polyfills
+            // in ESM builds since IE 11 can't even load them. However many of
+            // our users use bundlers to bundle ESM builds into IE 11
+            // compatible UMD builds. Therefore even ESM builds need IE 11
+            // polyfills.
+            esmodules: false
+          },
+          // This would pollute global scope. Babel's Transform Runtime plugin
+          // is used instead.
+          useBuiltIns: false
+        }
+      ]
+    ],
+    plugins: [
+      require("@babel/plugin-proposal-class-properties"),
+      require("@babel/plugin-proposal-object-rest-spread"),
+      [
+        require("@babel/plugin-transform-runtime"),
+        {
+          // Force corejs 3. The default corejs 2 is deprecated and doesn't
+          // contain some polyfills.
+          corejs: 3
+        }
+      ]
+    ],
+    env: {
+      test: {
+        presets: [
+          [
+            require("@babel/preset-env"),
+            {
+              // Tests run in Node so there's no need to include any other
+              // polyfills (we're testing our code, not the polyfills).
+              targets: "maintained node versions"
+            }
+          ]
+        ]
+      },
+      "test-cov": {
+        presets: [
+          [
+            require("@babel/preset-env"),
+            {
+              // dtto
+              targets: "maintained node versions"
+            }
+          ]
+        ],
+        // This instruments the code to record coverage. It's more reliable if
+        // done through Babel plugin.
+        plugins: ["istanbul"]
+      }
+    }
+  };
+
+  if (css) {
+    base.plugins.push(require("babel-plugin-css-modules-transform"));
+  }
+  if (ts) {
+    base.presets.push(require("@babel/preset-typescript"));
+  }
+
+  return base;
+};