20210114.184825.1dbe1be

modernize NSImage usage

- Fixes up NSImage to use a technique that doesn't depend on the
  DPI of the current screen and just uses pixels
- Fixes a crash when releasing the image; the crash was caused by
  a `memset` call getting a different size for the filename buffer.
  I solved this by passing the size down, which is safer than just
  assuming anyway.  I added an ASAN cmake option to make it easier
  to turn up the debugging and understand where the memory corruption
  had come from.

refs: https://github.com/wez/atomicparsley/issues/14