add dropbox support

maybe.

store markup content at dropbox.

append to the markup: createddate and date (modified date).

https://www.dropbox.com/developers/core

https://www.dropbox.com/developers/core/start/php

Perl:
https://github.com/s-aska/p5-WebService-Dropbox
https://github.com/norbu09/Net--Dropbox

http://search.cpan.org/~askadna/WebService-Dropbox-0.03/lib/WebService/Dropbox.pm
http://search.cpan.org/~norbu/Net-Dropbox-API-0.6/lib/Net/Dropbox/API.pm

*update 7aug2013:* may investigate this option later. 

#todo_later
#junco