Add a -Q option to perform complex saving requests

PR for #36

Add the following option:
-Q REQUEST, --request=REQUEST
save posts following the pattern TYPE:TAGS. TYPE can
be any, text, quote, link, answer, video, audio,
photo, chat and TAGS can be omitted. (TAGS can be
comma-separated values, pattern semicolon-separated
values) Example: "any:personal;quote;photo:me,self"