• Added an entry to CHANGELOG.md if this change could be valuable to users

This PR implements rendering of images in markdown views (hover, completion documentation, signature, and plugin readmes).

• The loading icon it shows is a bit weird, because typically you see them spinning
• Sometimes the images don't load???
  • I had this most often with the plugin readme (I put an image in my Aleph theme plugin's readme for testing).
  • I note that I have the same issue with plugin icons sometimes not loading, despite that they should be in the local cache folder by now. I'd think this was some github throttling (are those icons even hosted on github pages?), but it also happened for a local image (if less often??). I'm very confused.
• The positioning of images is off. This is mostly due to the code not paying attention to whether the user did a hard line break before the image or not. That'll have to be fixed for having links work in markdown views too.
• This provides an ImageCache.
  • Does not currently load SVGs, so it doesn't swap out the volt icon loading code to use image cache. (Though that should be possible, but I'm somewhat confused as to the best way to decide the size of an svg if it isn't literally given to us?)
  • Does not actually clear the cache yet. It keeps track of the data, but when I had it immediately remove with zero references I got failures to load an image a lot more often?