Added getter for elemsandsublayers to Layer class.
Added sublayerByElemsIndex to Layer class to return one of its sublayers using the sublayer's index in the elemsandsublayers array, which is the reverse order of the Layer class's sublayers array.
Added elemsIndex getter to Layer class to return the position of the layer in its parent layer's elemsandsublayers array.
Fixed Layer.elemsandsublayers to access the property through dom.frames.layers.
Fixed bug with accessing elemsandsublayers through frames on a sublayer.
Updated the layer module documentation.