0.20.4: zip / tar.gz / issues

Release Notes:

Upgrade Notes:

• Upgrading from 0.19 requires a full cluster restart.

Breaking Changes:

• Shared Gateway has been deprecated (2459)
• Snappy compression has been deprecated (2458)
• Plugins Installer: Allow to download plugins from download.elasticsearch.org (#2507)
• Sometimes MapperParsingException and sometimes not (#2354)

Bug fixes:

• Deb package wrongly includes additional lucene libraries (#2599)
• Support MultiPhrasePrefix (MatchQuery.Type.PHRASE_PREFIX) in Highlighters (#2596)
• Indexes created from index request might not replica initial doc to replica (#2594)