Hi there! This is Red Zebra - very simple text editor for iOS. It is heavily inspired by both GNU's NANO text editor and louisdh's Textor.
It's not meant to be a feature complete IDE, with fancy features and stuff... Just a simple tool that you use when you're away from your computer and need to review some code or update some variable value or what have you...
Master is the branch where all the new development is happening & it's version number should be close to the public beta.
The version that is on App Store is the "latest non-master branch" - for example: if there is branch named "1.2.9", that's the version that you can find on the App Store.
Master is most likely a little bit ahead of the App Store version - given our example probably something like 1.3 or 1.2.10.
(The first App Store version was 1.0. All the previous versions/branches were kinda random in-development branches)