Add a gitignore for Unreal Engine 4

UE4.gitignore

+# Compiled Object files
+*.slo
+*.lo
+*.o
+*.obj
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Compiled Dynamic libraries
+*.so
+*.dylib
+*.dll
+
+# Fortran module files
+*.mod
+
+# Compiled Static libraries
+*.lai
+*.la
+*.a
+*.lib
+
+# Executables
+*.exe
+*.out
+*.app
+*.ipa
+
+# These project files can be generated by the engine
+*.xcodeproj
+*.sln
+*.xcodeproj
+*.suo
+*.opensdf
+*.sdf
+*.sln
+
+# Precompiled Assets
+SourceArt/**/*.png
+SourceArt/**/*.tga
+
+# Binary Files
+Binaries/*
+
+# Builds
+Build/*
+
+# Don't ignore icon files in Build
+!Build/**/*.ico
+
+# Configuration files generated by the Editor
+Saved/*
+
+# Compiled source files for the engine to use
+Intermediate/*
+
+# Cache files for the editor to use
+DerivedDataCache/*