rewrite execercise generator using Moo*

Because of some limitations App::Math::Trainer is refactored using MooX::Cmd
and MooX::Options instead of shiny old App::Cmd.
modifying default for range being open ([0:)
removing MANIFEST from repo, update filter

removing generated file MANIFEST from repository, update filter
patterns in MANIFEST.SKIP
remove generated META.yml from repository
Enjoy the silence
add forgotten sub-command (.gitignore helps out)
also ignore output
add mandatory author tests
update requirements (after converting to MooX::*)
enable author tests in xt
some minor pod fixes
Bumping version to 0.002 for preparing a soon rel
add repository URI for meta data