Render parsed the layout and the page on every request, and a template that did not parse failed the first visit to its page rather than the process. All page templates now parse with the layout at package init and Render looks the page up; TestEveryPageTemplateParses asserts the set.
The nil-safe str/field helpers still render a misspelled field as absent; that is the layout's contract with page structs that do not share fields, and stays.
Closes #116