Siepic-ebeam-pdk

- contra-directional coupler PCell compact model generation using external python environment.

- updates to libraries to fix compatibility issues with KLayout 0.26

- new components to mature library (with CMLs)
++ sub-wavelength assisted coupler
++ adiabatic y_splitter 1x2

- metal pin snapping (merge pull request from S. Preble)

- new components to developers library
++ multiperiod bragg gratings
++ dual period contra-directional couplers
++ Sub-wavelength contra-directional couplers

- updates to scripted layout examples with additional examples

- added cross-section viewer

Updates:
* contraDC PCell
* New PCell to EBeam-dev: Period Chirped contra DCs
* Fix spiral waveguide PCell
* added 1310 nm waveguide
* added UGC (universal grating coupler) Pcell to dev library
* Calibre litho simulation layer
* ebeam_gc_te1550_broadband.GDS
* SWG rings, SWG_multibox_ring update, in EBeam-dev

Waveguide PCell: disable coerce, which strangely doesn't work when loading a layout.

- DRC files for UBC's ELEC463