Changed README with the current CLI options
Server allowed to be empty.

Nothing happens if server is empty or doesn't exist.
Custom targets.
Changed README to inform (briefly!) about targets.
If there is no public directy, don't try to change permissions.
Gemfile and Gemfile.lock checking

Just run bundle install if there is a Gemfile with a different MD5

Just run bundle install if Gemfile.lock exists and is writable

Just run bundle install if Gemfile.lock does not exists and current dir is
writable
Changed version number.