Round out the XSLT 1.0 stylesheet and output controls:
- xsl:include folds another stylesheet's templates, keys, globals, and output
at the same import precedence; xsl:import folds them one precedence lower,
so the importing stylesheet's rules win conflicts. Both resolve their href
through the injected document loader, never the filesystem.
- xsl:output drives serialization: method (xml or text), indent,
omit-xml-declaration, encoding, version, and standalone, layered over the
caller's emitter options. The text method emits character data only.
- xsl:comment and xsl:processing-instruction produce comment and PI nodes
from their instantiated bodies.
Templates now carry an import precedence that the matcher ranks ahead of
priority and document order.
Closes#64