Dependency and Metadata fixes.

When I wrote #17, I wrote the tests with the assumption `HTTP::Tiny::Mech` and `WWW::Mechanize::Cached` would be optional.

However, Autoprereqs has determined them to be mandatory, and this creates a few needless headaches installing dependencies. ( I personally get stuck somewhere because Cache::Cache fails )

So this patch rectifies this using `Dist::Zilla::Plugin::Prereqs::Soften` which moves the deps from `test.requires` to `test.recommends`.

However, at present, `test.recommends` vanish into a black hole, because `dist.ini` only uses `META.yml`, which only supports the `Meta 1.5` spec, and thus, only supports the old crufty options, and none of the new fancy stuff like 'recommends'. (  Amongst other things ).

While I was there, I noticed a great number of contributors presently go unrecognised ( `git shortlog` ), and so I added `[Git::Contributors]` to vivify `x_contributors` so that MetaCPAN can show them.