Performance Improvement and Refactoring

This release mainly improves performance, build tools, and codebase refactored using modern cpp17.
Here list out the changelog highlights:

• Fix: resolve w_m bug in ETF.cpp. #12
• Perf: minor optimizations. #26
• Refactor: remove PostProcessing class. 0757d53
• Refactor: remove cmath dependency. 2ca8e58
• Refactor: improve gui.{h,cpp} readability. #30
• Chore: properly add header guard.
• Chore: add Linux build scripts.
• Style: format code using clang-format.

for macOS pre-build, please use the terminal to run it: (usually require manually allow in Security Center)

$ ./Coherent-Line-Drawing