Not entirely related to the subject of OpenGL, but I really like how the author has decided to lay out this project. It's pretty hard to beat the convenience of a single header (or single header/single source) distribution for C libraries, but library development gets progressively harder as the project gets bigger as more code is added to the (usually hard to navigate) header file. Here, the author does their development with multiple files as one normally would, but when a new version is released they run the generate_gl_h[1] script that concatenates everything into a .h file for distribution. Simple yet flexible! This is also how SQLite[2] distributes its builds. It's a pattern that I'm using myself in some unreleased projects.
[1] https://github.com/rswinkle/PortableGL/blob/master/src/gener... [2] https://www.sqlite.org/amalgamation.html