[mythtv] Merging the 'render' branch

[Mark Kendall]

So after getting on for 600 commits and 11 months, I think the render
branch is ready for merging.

I've put a little more flesh on the bones of the wiki page (but it
still needs feeding):-

https://www.mythtv.org/wiki/2019-render

and the full gory detail is obviously available on github:-

https://github.com/MythTV/mythtv/tree/devel/2019-render

The great irony is that, after all those commits, a lot of people
won't notice any difference:)

Regardless, the new code should be leaner, more portable, more
extensible and more feature rich. It might even be faster.

There are still a few tweaks needed and I have a couple of clean up
commits to push but otherwise the database schema update required (for
video display profile settings) is already committed and ready to be
enabled (i.e. via a bump to the schema version).

Unless anyone has any serious concerns/objections, I will look to
merge it into master on Sunday. As Stuart has pointed out, we need to
give this a few months of stress testing before the next release.

Happy to answer any questions you may have.

Thanks all and regards
Mark