.epp should always be the preferred extension by convention

There are a handful of reasons for this, the primary reasons being consistency and ease of editor support. This is the recommended behavior with ERB which EPP should match for logical consistency in template handling. Support for the EPP syntax will need to be added to most common editors, and the `.epp` extension (or in this example `.html.epp`) is the easiest way to identify the syntax to use (rather than relying on magic comments or manual intervention).