Setting `=encoding` in I18n.pm's POD

The test `release-pod-syntax.t` was failing due to the UTF-8 chars in the
POD in this file.  Namely,

    RELEASE_TESTING=1 dzil test

showed up the problem.  This change corrects this issue by telling the POD
parser to expect UTF-8 text.
Adding missing POD to I18n.pm

Test::Pod::Coverage noticed a few undocumented methods; this change adds the
required text.  I tried to copy the existing POD documentation style as much
as possible, however if something needs correcting, I can update this commit
accordingly.
Removing PodCoverageTests from Dist::Zilla config

Now

    dzil test --author --release

runs without error.

The reason for this removal (which involves replacing the [@Classic] D::Z
plugin with [@Basic] and augmenting it to achieve the same behaviour,
however without PodCoverageTests) was that PodCoverageTests gave a warning
for *every* aliased Given/When/Then for *every* language...  The other
option would have been to maintain a `xt/pod-coverage.t` or similar which
then loads all possible language versions of Given/When/Then from the
`i18n.json` and tells Pod::Coverage to ignore them.  Also one would have to
tell D::Z not to generate `release-pod-coverage.t` etc...  In short, it
looks like the hassle of keeping PodCoverageTests seems higher than the
benefit it brought.
Merge pull request #37 from paultcochrane/ptc_pod_test_fixes

POD test fixes - thanks Paul