This implements just enough to get the path and header offset of each contained image.
It also adds a function to get an "any" File object for the image, so that the caller
doesn't need to write code twice for 32 and 64 bit images and can instead benefit from
the enum-based dynamic dispatch.
This commit also adds two "examples", for printing the list of images in the cache and
for dumping an object from inside the cache.

Use this for dyld cache image paths. The main benefit is avoiding
an artificial limit for mapped data.