✨ Add support for the CONDSTORE extension (RFC7162)

[nevans]

NOTE: Both #search and #uid_search have been updated to return SearchResult rather than Array. SearchResult inherits from Array, for backward compatibility.

Similarly, the MODIFIED response code on the tagged response to #store and #uid_store is currently only accessible by using a response handler: response code data on tagged responses isn't saved to #responses. Unlike with the search methods returning SearchResult, I did not change the behavior of #store to return a new result object inheriting from Array. IMO, that change would require a backward compatibility config option and a deprecation period.

• Fixes RFC7162 (2014): CONDSTORE (recommended by IMAP4rev2) #106
• Document IMAP extension support in Net::IMAP class rdoc
• New response codes (HIGHESTMODSEQ, NOMODSEQ, MODIFIED)
  • Parse (and test parser)
  • Document in ResponseCode
  • Update #select and #examine documentation (NOMODSEQ, HIGHESTMODSEQ)
  • Update #store and #uid_store documentation (MODIFIED)
    • Add SequenceSet class
      • basic version was added for ⚡ Better Faster Cleaner STATUS parsing #225
      • ✨ Improve SequenceSet with Set, Range, Enumerable methods #239
• Updated FETCH response with MODSEQ.
  • Parse (Done by @shugo in 2017, by 398a64e.)
  • Document in FetchData (Done by ✨ Add FetchData msg-att methods and update rdoc #220.)
• Updates SEARCH untagged response
  • Parse * SEARCH 1 2 3 (MODSEQ 123) (Done by @shugo in 2014, by 4bad059.)
  • Add SearchResult and SearchResult#modseq.
  • Document SearchResult (including on #search and #uid_search)
  • Basic test coverage over SearchResult code
• New HIGHESTMODSEQ status attribute
  • Parse (and test parser)
  • Document in #status
• Keyword args (and test client method calls)
  • Add condstore kwarg to #select, #examine (RFC7162, CONDSTORE) #122
  • Add changedsince kwarg to #fetch/#uid_fetch (RFC7162, CONDSTORE) #132
    (Note: CHANGEDSINCE can be used already, via an undocumented non-keyword argument.)
  • Add unchangedsince kwarg to #store/#uid_store (RFC7162, CONDSTORE) #237