Build: Adding .editorconfig file

Starting out with the rules we use from jquery-ui for consistency sake.
If we need to tweak these later, we can.
Closes gh-21

Author: sfrisk

.editorconfig

@@ -0,0 +1,16 @@
+# This file is for unifying the coding style for different editors and IDEs
+# editorconfig.org
+
+root = true
+
+[*]
+indent_style = tab
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[external/**]
+trim_trailing_whitespace = false
+insert_final_newline = varies
+end_of_line = varies