Change Play Perl to Questhub

This should close #1120
Merge pull request #1135 from book/questhub

Change Play Perl to Questhub
Generate sitemap for metacpan.org website

This introduces a script called bin/generate_sitemap.pl that creates XML files
containing URLs for authors, releases and modules; a module that does all of
the heavy lifting; a test script that exercies the module; and an updated
robots.txt file.
Also add ElasticSearch
Use FindBin to get lib path
Limit release to latest ones only

Previous version dumped all releases; releases are now limited to just the
latest ones, bringing that file in line with the size of the others.
Create xml.gz files, not just xml files
TidyAll
Use autodie.
Sort urls in sitemap.
Convert MetaCPAN::Sitemap to Moose.
Sitemap release URLs now point at /release/ rather than a download URL.
Generating sitemaps
Tidy everything.
generate sitemaps
Tidy everything.
Updated changes.
Code cleanup for sitemaps.
Only use the API message when we actually didn't get any raw content

Switches to checking the API response data rather than the stash after
processing through HTML::Restrict.  If HTML::Restrict fails, the lack of
pod may not be related to any API message.
Encourage folks to read the source when a file doesn't have any POD

Previously it rendered as "Error rendering POD for ... - ", with no
explanation.  See #1139.