Add editorconfig style for editors that support it.

.editorconfig

@@ -0,0 +1,15 @@
+# Copyright 2018 Rene Rivera
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE.txt or http://www.boost.org/LICENSE_1_0.txt)
+
+root = true
+
+[*]
+charset = utf-8
+indent_size = 4
+indent_style = space
+tab_width = 4
+trim_trailing_whitespace = true
+
+[*.yml]
+indent_size = 2