Port from Rust implementation

[chances]

• https://github.com/aeplay/descartes/blob/0f31b1830f15a402089832c7a87d74aba3912005/src/angles.rs
• https://github.com/aeplay/descartes/blob/0f31b1830f15a402089832c7a87d74aba3912005/src/convert_2d_3d.rs
• https://github.com/aeplay/descartes/blob/0f31b1830f15a402089832c7a87d74aba3912005/src/segments.rs
• https://github.com/aeplay/descartes/blob/0f31b1830f15a402089832c7a87d74aba3912005/src/rough_eq.rs
• Switch to https://gfm.dpldocs.info/gfm.math.shapes.html

[codecov-io]

Codecov Report

Attention: 77 lines in your changes are missing coverage. Please review.

Comparison is base (d50f778) 0.00% compared to head (60f69c5) 64.67%.

Files	Patch %	Lines
source/descartes/segments.d	52.94%	72 Missing ⚠️
source/descartes/angles.d	84.00%	4 Missing ⚠️
source/descartes/rough.d	94.11%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           master       #2       +/-   ##
===========================================
+ Coverage        0   64.67%   +64.67%     
===========================================
  Files           0        5        +5     
  Lines           0      218      +218     
===========================================
+ Hits            0      141      +141     
- Misses          0       77       +77     

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