Remove automatic lift:surround with="default" insertion

Remove automatic lift:surround with="default" insertion. Continue to
wrap Markdown templates in <html></html> if they contain multiple top
level nodes (but only if <html> is not already there).
Auto-surround top level Markdown templates

Auto-surround top level Markdown templates with default template and
refine test for top level templates
Clarify a boolean parameter by making it named.
Merge pull request #1604 from lift/pmb_surround

Remove automatic lift:surround with="default" insertion

Remove automatic lift:surround with="default" insertion, but wrap top level templates in
it if the template contains multiple top level nodes and does not already contain a surround.
This is necessary to support Markdown templates.