Locate binaries in a more portable manner

Currently, [Archive::Tar::Wrapper fails on Windows](http://www.cpantesters.org/distro/A/Archive-Tar-Wrapper.html#Archive-Tar-Wrapper-0.16?grade=1&perlmat=2&patches=2&oncpan=2&distmat=2&perlver=ALL&osname=mswin32&version=0.16 "Test Reports for Windows") because `::bin_find(...)` isn't very portable. `$ENV{PATH}` should be split with a semicolon (`;`), executable files should have an .exe extension, etc. Instead of doing the messy portability bits by hand, [File::Which](https://metacpan.org/module/File::Which) can be used to take care of all of that.