Add --dump to dump current frame to stdout

[ChillerDragon]

Using the elinks terminal browser you can view the full page rendered out as one text dump. Using this command for example:

$ elinks -default-mime-type text/html -dump -dump-charset UTF-8 https://duck.com
   Link: [1]canonical
   Link: [2]DuckDuckGo (Lite) (search)
   Link: [3]image_src
                                   DuckDuckGo

           [4]_________________________________________ [5][ Search ]

References

   Visible links
   1. https://duckduckgo.com/
   2. https://duckduckgo.com/opensearch_lite_v2.xml
   3. https://duckduckgo.com/assets/logo_homepage.normal.v101.png

Which is nice for the mutt email client. One can use the mailcap file to configure mutt to use a external tool to render out the html emails and then preview them in the terminal. Many modern emails are so bloated with html/css features that simple terminal browsers like elinks struggle. Using carbonyl to render emails in the terminal would be super useful for mutt users that receive fancy html mails.

Loosely related to #132