* Changed the passing of rgba_palette to a shared_ptr in order to better facilitate the use of a visitor pattern.
* Moved PNG util processing into its own set of files so that image_util_impl.hpp would not have to depend on HAVE_PNG.
* store image width and height in dimensions object
* allow specifying max_size for width and height (default 0xffff)
* throw if width or height are out of range - 0...max_size
avoiding one std::vector memory allocation - NOTE: this works because coordinates are stored in Double: Signed 64-bit IEEE double-precision floating point number (8 bytes) with little endian byte order - ref #2151
between inner and outter rings (Polygon/NultiPolygon) -- ref #2151https://github.com/mapbox/unpacker/issues/324
```txt
A polygon consists of one or more rings. A ring is a connected sequence of four or more
points that form a closed, non-self-intersecting loop. A polygon may contain multiple
outer rings. The order of vertices or orientation for a ring indicates which side of the ring
is the interior of the polygon. The neighborhood to the right of an observer walking along
the ring in vertex order is the neighborhood inside the polygon. Vertices of rings defining
holes in polygons are in a counterclockwise direction. Vertices for a single, ringed
polygon are, therefore, always in clockwise order. The rings of a polygon are referred to
as its parts.
```
between inner and outter rings (Polygon/NultiPolygon) -- ref #2151https://github.com/mapbox/unpacker/issues/324
```txt
A polygon consists of one or more rings. A ring is a connected sequence of four or more
points that form a closed, non-self-intersecting loop. A polygon may contain multiple
outer rings. The order of vertices or orientation for a ring indicates which side of the ring
is the interior of the polygon. The neighborhood to the right of an observer walking along
the ring in vertex order is the neighborhood inside the polygon. Vertices of rings defining
holes in polygons are in a counterclockwise direction. Vertices for a single, ringed
polygon are, therefore, always in clockwise order. The rings of a polygon are referred to
as its parts.
```
