Now that Lektor supports Python 3, we need to document this support.
This change is perhaps a bit extreme: it replaces all explicit
references to Python 2.7 with explicit references to Python 3.5.
However, it's a good start, and it can and should be reviewed before
being merged.
Joseph Nix
Mark Steve Samson
David Baumgold
Gunbei
Brian Cappello
Armin Ronacher