Pull Request Note
If you're reading this, you were probably linked here from a pull request. If this is not the case, this article probably won't be of any use to you!
sampctl is a Pawn development tool. The files in the pull request exist to make installing and using the library much easier than the traditional method. pawn.json is the most important part here, I may have also modified the README.md file to include sampctl package install <package name> installation instructions.
sampctl is designed so you don't need a pawn.json ("Pawn-Package Definition" file) in every repo, but having it there really helps with dependency management! These changes are purely additive and do not change your code or scripting style in any way, you don't need to use sampctl yourself but I encourage you to give it a try!
This makes all .pwn and .inc files appear as Pawn files to GitHubg instead of SourcePawn - this makes your package appear on http://packages.sampctl.com so users can easily find it by searching and sampctl will also auto-complete when a user partially types the package name in sampctl package install.
This pull request may have also added a file called test.pwn, this file is known as an "entry script" and enables the code to be run and tested very quickly by simply running sampctl package run.