siepic.extend.find_components function, subcells

[lukasc-ubc]

Limitation of this function:

• it requires that the DevRec and PinRec shapes be in the highest level of the component's hierarchy. In the example below, the component was embedded inside another top cell with a different name. find_components does not find it, and connecting waveguides / components via script doesn't work.
• considering adding "raise Exception", as this should only occur in coded layouts.

PDK developers should be aware of this limitation. Update documentation.