Create .editorconfig

Add .editorconfig with the same rules from https://github.com/documentationjs/documentation/blob/master/.editorconfig - but with addition of HTML. Helps keep code consistently formatted :-)

Author: coliff

.editorconfig

@@ -0,0 +1,4 @@
+[*.{js,css,html}]
+indent_style = space
+indent_size = 2
+trim_trailing_whitespace = true