delay evaluating the template until munging time

This postpones the execution of $zilla->version, which might not be calculable
if other files have not yet been added to the dist.
The file is saved locally so it can still be found even if it was renamed in
the interim, e.g. via [ExtraTests].
switch from Path::Class to Path::Tiny
modernize repo; use explicit VERSION
get rid of WikiDoc in Pod
update Changes
.travis.yml