Optimization: Dynamically adjust fill width and spacing when filling narrow gaps.

[Lodran]

When generating infill for a narrow gap (one that is wider than one filament, but narrower than two), center the filament within the gap, and adjust the filament width to compensate.

[triffid]

this is an awesome idea, I vote for this

[triffid]

Here's a situation where this feature would have been really handy:

https://picasaweb.google.com/lh/photo/xdTRmlYadAGP37cyYzk7KtMTjNZETYmyPJy0liipFm0

The gap there is much bigger than one extrusion width, but just slightly smaller than two, so it gets left unfilled. Not a problem with this particular model, but could definitely be problematic with other things

[alranel]

Actually, this was done recently but I didn't remember there was an issue. Flow is auto-adjusted for all solid fills to avoid side gaps. Also, small regions are infilled as solid.