Kratos

Fixed
- Fix the same bug in mixed assignment check where a slice will trigger false positive result

Fixed
- Fix a bug in multi-driver detection where a slice will trigger false positive result

Added
- Add ability to generate old-style Verilog based on `sv2v`
- Add SRAM library generation as a native lib
- Add flatten pass to flatten N-D array for tools that don't support it
- Add a pass to extract registers names from the design

Changed
- Drop Python 3.5 support
- Lower MacOS version requirement, thanks to miniconda
- Improved ternary code generation
- Loose decouple ports requirements (132)

Fixed
- Adjusted python pass order to check connectivity first before decouple the wires
- Get def instance if all the instances linked in the graph is cloned (133)

Added
- Allow normal values to be casted to enum;
- Add strict type checking
- Add pass to check combinational loop (87)
- Add raw string statement
- Add windows build and native wheel (131)

Changed
- Remove old verilog generation requirements
- C++ enum is now enum class

Fixed
- Fix filesystem detection code on gcc-8

Added
- Use BSD-2 license
- Add a pass to detect multiple drivers
- Upload src files to pypi

Changed
- Use old mac-os image but switch to gcc-8 for consistent result
- Refactor `always` to `always_comb` and `always_ff` for better semantics, and add warnings
if absent.
- Python based tests are refactored to re-use pytest fixtures

Fixed
- Fixed a bug in var high calculation when the parent is a slice
- Various interface bug fixes

Added
- Add helper function to expose kratos interface to magma

Changed
- Change port_type and port_direction to property in Python binding