Adds a procedure to upgrade CNXML documents to CNXML verison 0.7.
Merge pull request #27 from Connexions/cnxml-upgrade

Adds a procedure to upgrade CNXML documents to CNXML verison 0.7.
Add --force flag to overwrite index.html in cnx-upgrade to_html

Enable this flag means that the index.html will be removed before a new
one is generated.