Custom keyboard shortcuts
####Example ```javascript var testEditor = editormd("test-editormd", { width: "90%", height: 720, path : '../lib/', onload : function() { var keyMap = { "Ctrl-S": function(cm) { alert("Ctrl+S"); }, "Ctrl-A": function(cm) { // default Ctrl-A selectAll // custom alert("Ctrl+A"); cm.execCommand("selectAll"); } }; // setting signle key var keyMap2 = { "Ctrl-T": function(cm) { alert("Ctrl+T"); } }; this.addKeyMap(keyMap); this.addKeyMap(keyMap2); this.removeKeyMap(keyMap2); // remove signle key } }); ```