Complex requests

PR for https://github.com/bbolli/tumblr-utils/issues/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"