Ignore tiled xml data in csv tilemaps

this pull adds a way to ignore leading and trailing xml created by the tiled map editor in FlxTilemap. This was an unintended benefit of my previous pull, but it turned out that that was actually not loading in the entire map if there was xml....thats what you get for not thoroughly checking out why exactly something is happening, even if it seems beneficial.
hope this helps,
Nico