Better build process (#1248)

* Remove gulp, replace with custom scripts
* Symlink entire dirs where possible (fixes #1232)
* Significantly speed up subsequent builds (fixes #1238)
* Watch process now observes new/removed files, not only changed
* Add ignoreMask, exclude all files with names starting with a #
* Better logging during builds
* Update travis.yml to use new, non-gulp-based build

scripts/babel-worker.js

@@ -0,0 +1,56 @@
+/* global onmessage: true, postMessage: false */
+'use strict';
+
+const fs = require('fs-extra');
+const path = require('path');
+const babel = require('babel-core');
+const multimatch = require('multimatch');
+const options = JSON.parse(fs.readFileSync('.babelrc'));
+const cluster = require('cluster');
+
+/* exported onmessage */
+async function babelWorker(ev) {
+	const t1 = Date.now();
+	const sourcefile = ev.file;
+	const outfile = path.join('build', sourcefile);
+	const postError = (error) => {
+		process.send({
+			sourcefile,
+			outfile,
+			error
+		});
+	};
+
+	var isSkipped = false;
+	var transformed;
+
+	try {
+		let contents = await fs.readFile(sourcefile, 'utf8');
+		if (sourcefile === 'resource/react-dom.js') {
+			// patch react
+			transformed = contents.replace(/ownerDocument\.createElement\((.*?)\)/gi, 'ownerDocument.createElementNS(DOMNamespaces.html, $1)');
+		} else if ('ignore' in options && options.ignore.some(ignoreGlob => multimatch(sourcefile, ignoreGlob).length)) {
+			transformed = contents;
+			isSkipped = true;
+		} else {
+			try {
+				transformed = babel.transform(contents, options).code;
+			} catch (error) { return postError(`Babel error: ${error}`);}
+		}
+
+		await fs.outputFile(outfile, transformed);
+		const t2 = Date.now();
+		process.send({
+			isSkipped,
+			sourcefile,
+			outfile,
+			processingTime: t2 - t1
+		});
+	} catch (error) { return postError(`I/O error: ${error}`); }
+}
+
+module.exports = babelWorker;
+
+if (cluster.isWorker) {
+	process.on('message', babelWorker);
+}