move xt tests to xt/author for Module::Install to work

diff --git a/xt/pod-coverage.t b/xt/author/pod-coverage.t
similarity index 100%
rename from xt/pod-coverage.t
rename to xt/author/pod-coverage.t

diff --git a/xt/pod-spell.t b/xt/author/pod-spell.t
similarity index 100%
rename from xt/pod-spell.t
rename to xt/author/pod-spell.t

diff --git a/xt/pod.t b/xt/author/pod.t
similarity index 100%
rename from xt/pod.t
rename to xt/author/pod.t

diff --git a/xt/tabs.t b/xt/author/tabs.t
similarity index 100%
rename from xt/tabs.t
rename to xt/author/tabs.t

diff --git a/xt/version-numbers.t b/xt/author/version-numbers.t
similarity index 100%
rename from xt/version-numbers.t
rename to xt/author/version-numbers.t