refactor selection support into a separate class

Merge branch 'master' into HEAD

Conflicts:
	src/Editor.js
	src/KeyBinding.js
	src/Selection.js

src/TextDocument.js

@@ -3,6 +3,7 @@ ace.provide("ace.TextDocument");
 ace.TextDocument = function(text) {
     this.lines = this._split(text);
     this.modified = true;
+    this.selection = new ace.Selection(this);
 
     this.listeners = [];
 };
@@ -15,6 +16,10 @@ ace.TextDocument.prototype.toString = function() {
     return this.lines.join("\n");
 };
 
+ace.TextDocument.prototype.getSelection = function() {
+    return this.selection;
+};
+
 ace.TextDocument.prototype.addChangeListener = function(listener) {
     this.listeners.push(listener);
 };