graphics/aloadimage: add new port
Aloadimage is a simple command-line imageviewer for arcan, built on
the image parsers provided by stb. Image loading is performed in the
background as a separate, sandboxed (on Linux) processes and should be
reasonably safe against maliciously crafted input sources.
The primary purpose is to provide an arcan- specific replacement for
xloadimage, and to serve as a testing ground for advanced image output such as
full HDR- paths. The secondary purpose is to craft the image- loading worker
pool to be secure and efficient enough to act as a building block for other
components within the Arcan umbrella.