Explicit Muxes in Scan-chain and SCL Configuration YAMLs (#40)
* Created YAML configuration file for supported SCLs with the ability to define:
* D-flipflops and their D/Q portnames (if for some godforsaken reason the ports are not named D and Q)
* Optionally, a multiplexer to use for scan-chain stitching
* If the multiplexer exists, it takes priority, otherwise, a ternary operation is used
* Updated Swift requirement to 5.4+
* Updated macOS requirement to 11+
* Ran [SwiftFormat](https://github.com/nicklockwood/SwiftFormat)'s default ruleset on all files.
