PYTHON.jsonversion bumped from 2 to 3 in order to define location of
- Tcl/tk support on Linux and macOS builds. (Windows support is coming.)
- Zstandard compression on tarballs increased to result in archives ~50% of original size.
- Various files in tarballs are now symlinks instead of copies of the same file.
- SQLite version updated from 3.28 to 3.29.
- bzip2 version updated from 1.0.6 to 1.0.8 (includes a security fix).
- macOS now built with Clang/LLVM 8 instead of Clang/LLVM 6.
- Build systems for Linux and macOS unified.