Added first simple 'marker' support

Simple addition of markers (in order to highlight text or other stuffs). Floating markers are markers that are "bound" to a text. If any moficiation (insert/delete) is performed, the marker is updated.

Currently, markers have to be handle by the user (by keeping markerID somewhere). 

Here is an example for markers:
```java
AceRange mark = AceRange.create(2, 0, 2, 10);
int id = editor.addMarker(mark, "ace_selected-word", AceMarkerType.TEXT, true);
editor.removeMarker(id);
```

and another example for floating markers:
```java
AceRange mark = AceRange.create(2, 0, 2, 10);
int id = editor.addFloatingMarker(r, "ace_selected-word", AceMarkerType.TEXT);
mark.detach();
editor.removeMarker(id);
```