Add an .editorconfig file

What is .editorconfig:
http://editorconfig.org/#overview

Plugins for IDEs to support:
http://editorconfig.org/#download

.editorconfig

+# EditorConfig is awesome:
+http://EditorConfig.org
+
+# top-most EditorConfig file
+root = true
+
+# Default settings:
+# Use 4 spaces as indentation
+[*]
+indent_style = space
+indent_size = 4
+
+# Xml project files
+[*.{csproj,vbproj,vcxproj,vcxproj.filters,proj,projitems,shproj}]
+indent_size = 2
+
+# Xml config files
+[*.{props,targets,ruleset,config,nuspec,resx,vsixmanifest,vsct}]
+indent_size = 2