Break out a command-line package

[dan-fritchman]

The Hdl21SchematicEditor is thus far broken into these sub-packages:

• EditorCore provides the core editor functionality.
• EditorApp exposes the editor as a standalone desktop application, using the Electron framework.
• VsCodePlugin exposes the editor as a VS Code plug-in.
• PlatformInterface defines the interface between EditorCore and its underlying "platforms", i.e. the other packages.

Two prospective additions stand out:

1. The web platform/ instance #10
2. A "command-line" platform, which does not render anything graphically or use the DOM, but could do things like:

• Perform schema checking
• Export schematics to other formats
• Perform schema migrations
• etc

This would also seem to help with #9.

[dan-fritchman]

Another thing I suppose one could do:
Create schematics from circuits - e.g. as commonly done for debugging - without needing the SVG syntax.