Introduce .editorconfig (#149)

.editorconfig will allow maintaining consistent coding style across
various text editors and IDEs

.editorconfig

@@ -0,0 +1,14 @@
+# EditorConfig helps developers define and maintain consistent coding styles between different editors and IDEs
+# @see http://editorconfig.org
+root = true
+
+[*]
+end_of_line = lf
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+indent_style = spaces
+tab_width = 2
+
+[{*.{rb,erb,js,coffee,json,yml,css,scss,sh,markdown,md,html}]
+indent_size = 2