Clean up perl API dependencies

If we assume a non-ancient perl (>=5.8.1), we can clean up the dependencies:

(build) Module::Install: bundle it
(build) Module::Install::ReadmeFromPod: keep
(build) Module::Install::Repository: remove, hardcode repository value instead of autodetecting
(build) Test::More 0.88: keep, but note requisite version built in starting at 5.10.1
(test) Test::Exception: keep
(test) Test::Pod: declare (missing in Makefile.PL)
(test/run) Math::BigInt: don't declare, now built-in
(run) JSON::XS: replace with JSON to not tie to a backend
(run) parent: keep, but note built-in starting at 5.10.1
(run) Compress::Zlib: keep, but note built-in starting at 5.9.3
(run) IO::String: replace with perl 5.8 functionality
(run) Encode: don't declare, now built-in
(run) Regexp::Common: keep
(run) Object::Tiny: keep
(run) Try::Tiny: keep