Set a variable if we're building for the live docs site or not

This is useful to customize online / offline search and whether to
include things like Google Analytics.

Fixes #9875
Merge pull request #12096 from UtahDave/develop

change windows downloads to use https
Merge pull request #12097 from whiteinge/docs-ga-opt-in

Set a variable if we're building for the live docs site or not
Added Mine example with arguments

Closes #11227
add links to the md5 hash files
add note about comparing md5 hashes