add docopt parser to prepare for gem compilation
update tagger to remove 404 pages, and to tag images
reorganized for gem spec; added gem spec file
Merge branch 'feature/prepare_for_gem' into develop

Conflicts:
	lib/pinboard_tools/pinboard_tagger.rb
update requirements
changed logic of parsing; added fallback to all posts on empty tag command
add error for empty credentials file
add error message to options parser
add ignored file types
add verbose options to safari importer
add verbose option to safari command
updated readme file
changed executable name
add github page as gem homepage
upadted readme
Merge branch 'release/0.4'