marker-layer: added alignment for markers
With the here implemented properties xalign
and yalign
of
Shumate.MarkerLayer, implementors can now exactly specify how their
markers are to be aligned on the map.
This is particulary useful for normal "pin"-inspired markers, as they have
the position they're supposed to represent on the bottom of the marker
instead of the center. This is currently causing these kind of markers
to be misaligned.