The memory, in bytes, of the loaded images kept in memory and shared by every
MarkdownViewer, so that rendering an image again (a document edited and
re-rendered, a viewer recreated) neither downloads nor decodes it again. A bitmap counts 4 bytes
per pixel, and any other image as much as a bitmap of its size. Images are keyed by their resolved
URL and the image loaders in use; the least recently used one is evicted first. An image heavier
than a tenth of the size is not cached, so the cache always has room for ten images. 0
disables the cache. Defaults to 100 MB. Lowering it evicts the images beyond the new size.
public static long ImageCacheSize { get; set; }