Big change in SKiDL development branch!

[devbisme]

The change: I moved the schematic generation code from SKiDL into the separate schematizer package. SKiDL now generates KiCad schematics and SVGs by passing a vendor-neutral netlist to schematizer. There is no change from the standpoint of a user trying to generate schematics; the generation just happens in another place.

Reasons for the change:

1. Decouple schematic generation code from SKiDL so each can move at its own pace.
2. Support multiple, independent techniques for schematic generation.
3. Create a tool that others could use to generate schematics outside of SKiDL.
4. Implement an interface through which SKiDL could generate schematics using tools from others.