APA.pm: Double encoding can occur in when Keywords contains spaces on ItemSearches.
  The reason for this is because sub query_form (URI::_query) turns
  ' ' into '+'. URI::Encode::uri_unescape does _not_ turn '+' into ' '
  and so when sub sign (URI::Amazon::APA) runs query_form again to append
  the signature, query_form loops through and turns all '+'s into '%2B's.

  The best case scenario would be to make query_form act like URI::Encode.
Merge pull request #1 from nilnilnil/caine/keyword-double-encode

APA.pm: Double encoding can occur in when Keywords contains spaces on It...