Add Enter the Gungeon

[just-ero]

If you are adding or modifying an Auto Splitter, please fill out this checklist:

• My Auto Splitter does not contain any malicious functionality and I'm entirely responsible for any damages myself. (Any kind of abuse in an Auto Splitter will result in an immediate ban.)
• I am not replacing an existing Auto Splitter by a different author, or I have received permission from the author to replace the existing Auto Splitter.
• The Auto Splitter has an open source license that allows anyone to fork and host it.