additions from backlog and conversions to git

entries/sludge.md

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+# Sludge
+
+_Adventure game engine._
+
+- Home: https://opensludge.github.io/
+- State: mature
+- Download: https://opensludge.github.io/download.html, https://github.com/opensludge/opensludge/releases
+- Platform: Windows, Linux, macOS
+- Keywords: game engine, adventue
+- Code repository: https://github.com/opensludge/opensludge.git
+- Code language: C, C++, Objective-C
+- Code license: LGPL-2.1
+- Code dependencies: GTK
+
+## Building
+
+- Build system: Make