added P<doc:> and P<file:>

This maybe is not best implementation but allows to include pod files and modules (including declarative doc). It's manually merged from here https://github.com/teodozjan/pod-to-text2/
I'd go with `return EVAL slurp($path) ~ "\n$=pod"` sooner than calling `qqx`. It's unfortunate it has to be hacky either way... perhaps we an `EVAL :lang<doc>` or some such is in order...