Adds additional information to the stackviz-export and stackviz-front
technical documents. Info about `stackviz-export` output files is
now included in the corresponding document. Directive and service
descriptions were added to stackviz-front, alongside inline comments
in the appropriate .js files.
Due to the unique structure of GitHub's RST renderer, includes will
no longer be used in the main README.
Change-Id: Iaebf1f1c3b5e4cbb4ea5e262f85672bc082bbe2f
e3af3b2bd3