Use Path::Tiny instead of File::Slurp and File::Basename.

File::Slurp has some sort of potential Unicode security problem, but
really this is an excuse to get rid of the salad of File modules in
favor of Path::Tiny.  Path::Tiny is the all in wonder file handling
module.

See https://rt.cpan.org/Ticket/Display.html?id=100030
Merge pull request #177 from plu/refactor/Path-Tiny

Use Path::Tiny instead of File::Slurp and File::Basename.