Add a development server

[jplatte]

• using hyper, tower-http, minijinja-autoreload, inotify
• optional at compile time
  • it should still be hinted at in --help output if compiled out
• debounce inotify events required to handle file moves correctly? (consider public path remains the same, could there be spurious conflicts?)

[MTRNord]

On the debouncing: in zola usually when changing the git branches while zola serve is running it breaks itself and needs a new change event to unbreak. So it would be nice if this somehow could be avoided

[jplatte]

hinoki serve has been a thing for a little while now. It doesn't do incremental rebuilds yet, there's also a small known bug (#30) but it's there.