Build ECMAScript modules (#1479)

* Separate type import statement from module import statement

* Remove extension from import statements

* Build ECMAScript modules

* Add `cross-env` devDependency

* Use `babel-plugin-import-rename` instead of custom plugin

* Improve `.babelrc` style and add comments

* Update README.md

* Change file extension to `.mjs`

Comply with Node.js spec. Use extensionless package:main.

* Enforce only ESM compatible imports

* Dedupe packages

* Add `unicodeMake.js` to overrides:excludedFiles

* Fix .eslintrc merge conflict

* Use rollup to bundle ES module

* Remove `eslint-plugin-import`

* Change build directory to `dist`

* Change build directory to `dist`

* Change build directory

* Move docs from README.md to browser.md

* Update update-sri.js

* Revert update-sri.js

* Revert update-sri.js

* Update .eslintrc

* Remove SSH key testing

package.json

@@ -2,7 +2,8 @@
   "name": "katex",
   "version": "0.11.0-pre",
   "description": "Fast math typesetting for the web.",
-  "main": "dist/katex.js",
+  "main": "dist/katex",
+  "module": "dist/katex.mjs",
   "repository": {
     "type": "git",
     "url": "git://github.com/Khan/KaTeX.git"
@@ -51,6 +52,8 @@
     "postcss-loader": "^3.0.0",
     "query-string": "^6.1.0",
     "rimraf": "^2.6.2",
+    "rollup": "^0.63.4",
+    "rollup-plugin-babel": "^3.0.7",
     "selenium-webdriver": "^3.6.0",
     "sri-toolbox": "^0.2.0",
     "style-loader": "^0.22.0",
@@ -81,7 +84,7 @@
     "prestart": "node check-node-version.js && check-dependencies && node src/unicodeMake.js > src/unicodeSymbols.js",
     "start": "webpack-dev-server --hot --config webpack.dev.js",
     "analyze": "webpack --config webpack.analyze.js",
-    "build": "yarn prestart && rimraf dist/ && mkdirp dist && cp README.md dist && webpack",
+    "build": "yarn prestart && rimraf dist/ && mkdirp dist && cp README.md dist && rollup -c && webpack",
     "watch": "yarn build --watch",
     "dist": "yarn test && yarn build && yarn dist:zip",
     "dist:zip": "cd dist && tar czf ../katex.tar.gz * && zip -rq ../katex.zip *"