include: make header guards more sane The C++ standard[1] says: Each identifier that contains a double underscore __ or begins with an underscore followed by an uppercase letter is reserved to the implementation for any use. [1]: https://timsong-cpp.github.io/cppwp/n4659/lex.name#3.1

# Icons
These icons are from Yusuke Kamiyamane's [[Fugue Icons]](https://p.yusukekamiyamane.com/) pack. The original files have been left intact alongside bin2h variants (for easy inclusion in source code).