Problem description

There are a number of links in the Sphinx and Doxygen docs that link to the current version of the Cantera website, but need to be updated for the Cantera 3.1 release where this layout will change. A couple examples:

• Link to "Reactor Science" on this page (comes from description in ReactorBase.h.
• Links to YAML user guide / convert docs on this page (comes group description in global.h)

A regex search for cantera.org/(?!license) finds the cases where the fully qualified URL is used. Searches for /html/, /science/, and /sphinx/ also help find some things that need to be updated (but not all -- some of these are links to docs for specific versions of cantera, which should remain at the same location)