Add --build command

First pass at the build system described in #356.

To test it, move to a new, empty directory and try `tiddlywiki
editions/tw5.com --verbose --build`

core/modules/commands/build.js

@@ -0,0 +1,52 @@
+/*\
+title: $:/core/modules/commands/build.js
+type: application/javascript
+module-type: command
+
+Command to build a build target
+
+\*/
+(function(){
+
+/*jslint node: true, browser: true */
+/*global $tw: false */
+"use strict";
+
+exports.info = {
+	name: "build",
+	synchronous: true
+};
+
+var Command = function(params,commander) {
+	this.params = params;
+	this.commander = commander;
+};
+
+Command.prototype.execute = function() {
+	// Get the build targets defined in the wiki
+	var buildTargets = $tw.boot.wikiInfo.build;
+	if(!buildTargets) {
+		return "No build targets defined"
+	}
+	// Loop through each of the specified targets
+	var targets;
+	if(this.params.length > 0) {
+		targets = this.params;
+	} else {
+		targets = Object.keys(buildTargets);
+	}
+	for(var targetIndex=0; targetIndex<targets.length; targetIndex++) {
+		var target = targets[targetIndex],
+			commands = buildTargets[target];
+		if(!commands) {
+			return "Build target '" + target + "' not found";
+		}
+		// Add the commands to the queue
+		this.commander.addCommandTokens(commands);
+	}
+	return null;
+};
+
+exports.Command = Command;
+
+})();