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/clean.js

@@ -0,0 +1,26 @@
+'use strict';
+
+const path = require('path');
+const fs = require('fs-extra');
+const { onError } = require('./utils');
+
+const ROOT = path.resolve(__dirname, '..');
+
+async function getClean(source) {
+	await fs.remove(source);
+}
+
+module.exports = getClean;
+
+if (require.main === module) {
+	(async () => {
+		try {
+			await getClean(path.join(ROOT, 'build'));
+			await getClean(path.join(ROOT, '.signatures.json'));
+		} catch (err) {
+			process.exitCode = 1;
+			global.isError = true;
+			onError(err);
+		}
+	})();
+}