More robust file serving, Sony IP cam compatibility

• Implement ../PATH and ./PATH URLs relative to Cacao's program file.
• Use MJPEG DataLen header if Content-Length doesn't exist.
• Make serveFile send 404's and directory index based on the filesystem contents.
• Send no-cache headers from serveHttp.

Have fun,
Michael.

Fixes and Chrome/Firefox MJPEG.

• Fix HTTP proxy connection leak.
• Improve file proxy error messages.
• Get mjpeg.html working on Firefox and Chrome without relying on nonstandard behaviour.

Have fun,
Michael.

Welcome to Cacao!

An exploratory release to provide a baseline that we can use for other frontends.

• Crib pub run grinder package from dart-sass.
• Clean up serve API in preparation for UI development.

Please try it out if you're brave, and post any issues you find!

Thanks,
Michael.