Serve static pages efficiently. Fix #53

[HHHartmann]

Allows to load up to 5 static URLs at the same time.
The limit of 5 seems to be imposed by the system.

This should at least partially fix #53

[HHHartmann]

anybody willing to review this?

[marcoskirsch]

I will soon, my bad.

[Fractal147]

Err, while this achieves the goal, can't you achieve most changes from within httpserver-static.lua? You can access the socket within bufferedConnection, and yield there - no buffer used, no problem.

The chunks are 1024 big, but have no buffer to worry about since it's never filled
There are further things to do, like setting req=nil in httpserver.lua for static, but this seems pretty efficient to me - and works with 5 cars on chrome desktop.
See PR #123

[HHHartmann]

The main advantage in this PR is to get rid of the coroutine overhead which seems to be quite large.
The rest might be done differently. But what seems important to me is that the memory footprint between sending chunks is minimal (only filename and position) which helps executing several requests at the same time.