Schematic fixes

[IJeffray]

Several small but significant improvements to schematic conversion

• Cope with SCHDOC files filenames case-insensitively (this fixes top level sheet references)
• Add support for ports
• Add support for sheet entries
• Add 'rough' support for elliptical arcs (ignoring the 2nd radius, but useful/perfect for some symbols)
• Improve reference labels (eg =Value)
• other minor "implementation level" fixes to reduce code level warnings

[thesourcerer8]

Great! Lots of improvements! Nice! Could you please add warnings for the Ellipses again, so that people know what they have to review?

[IJeffray]

Elliptic arc warnings - wilco (but this is no different to other entities which have some params ignored...) Arcs need more work anyway - I'm looking at this just now, as I've inductors that come out like wobbly worms rather than loops.

[thesourcerer8]

Ah, we are talking about schematics, I thought this is about PCB. Ok, there I think we don't need warnings for ellipses. But on the other hand, it might be a good idea anyway. I was thinking about PCBs, where I had troubles with octagonal pads, and if I had converted them to a different shape (circle or rectangular), they would have caused short-circuits with neighbor pads, or would have been too small. So the only way out was to warn the users that they must review it since the conversion would most likely cause troubles. If you find anything where missing parameters could cause real problems, feel free to add warnings. I've been thinking about some kind of warning mode, where we add some warning symbols or something so that the place where the warning belongs to can be more easily found.