Ignore data, keep data directory

Author: brylie

.gitignore

@@ -160,3 +160,9 @@ cython_debug/
 #  and can be added to the global gitignore or merged into this file.  For a more nuclear
 #  option (not recommended) you can uncomment the following to ignore the entire idea folder.
 #.idea/
+
+# Ignore all files in the data directory
+data/*
+
+# But do not ignore the .gitkeep file
+!data/.gitkeep