Optionally parse with JSON::PP

[XanC]

In upgrading from Debian Wheezy to Debian Stretch, I found that my script that runs WebService::Solr no longer worked: JSON::XS in WebService::Solr::Response always failed to parse the response, even when the response was perfectly valid. I believe this is because my script is multi-threaded, and JSON::XS is not guaranteed thread-safe. JSON::PP works perfectly.

This pull request implements an option to allow WebService::Solr to use JSON::PP. There may be a better way of achieving this.

Thank you for WebService::Solr!

[petdance]

Thanks for looking into this. It seems like a reasonable thing to want.

I can't use this PR as-is because there are no tests and no updates to documentation to explain to the user how to use the new functionality.

[XanC]

Thanks. I've added a documentation line describing the new PP option. Also I created a new PP version of each test that called WebService::Solr->new(), modifying each one to enable the PP option.