Make PCell writing easier

[DerekK44]

Writing python scripts to make PCells should be easy. In principle, it should consist of only:

1. Drawing the shapes on the appropriate layers, with as much or as little parameterization as needed
2. Specifying the location and names of the ports

Everything else (handling cell and shape rotations, naming the cell, etc.) should be handled automatically. I think it would be best if all the components inherit from a new PICwriter component class (which then inherits from the gdspy Cell class), to handle all of these events in a standard format.

Once this is done, it would be great to add a page to the documentation with a tutorial on writing custom PCells.

[DerekK44]

This has been implemented in the recent commits, by transitioning all components to a custom Component class in the toolkit. A proper tutorial still needs to be added to the docs...

[gyger]

Is there a reason this component class does not inherit from gdspy.Cell?