Fix role filtering documentation code examples.

The role filtering documentation code samples do not format properly on
the documentation website. This pull request fixes that.
Merge pull request #47 from forward3d/fix_role_filtering

Fix role filtering documentation code examples.
Apply filtering doc changes in Jekyll
Updated the heredoc example in Capistrano 3 release announcement to be more explicit about a caveat with SSHKit adding `;` if `then` is followed by a newline (fixes capistrano/capistrano#812)
Fix typos in authentication and authorisation
small fix in the shell mode docs
Merge pull request #51 from plentz/patch-1

small fix in the shell mode docs
Merge pull request #52 from rampantmonkey/typos

Fix typos in authentication and authorisation
change meta 'role :all' to legal 'role :web'

This typo costed a lot of my time.
See https://github.com/capistrano/capistrano/pull/711 for more details.
Merge pull request #55 from sergey-alekseev/master

change meta 'role :all' to legal 'role :web'
added documentation to allow using capistrano from ruby script
cleanup of installation notes

Remove obsolete text about to-be-released v3 gem.
tightened up the requires, the default capistrano/rails does it all
interested people can go to the respective READMEs
fix backticks that did not render code

i <3 documentation!
Merge pull request #59 from tilsammans/updated-installation-instructions

cleanup of installation notes
Indicate how to add github.com to the list of server known hosts.
Add -p option on mkdir command

Else the `mkdir -p ${deploy_to}` fails on my system because `/var/www/` did not exist.
Indicate to require 'capistrano/rails' after 'capistrano/deploy'
Merge pull request #62 from Florent2/patch-3

Indicate to require 'capistrano/rails' after 'capistrano/deploy'
Add the capistrano v3 way of using gateway servers

This is based on the discussion in
https://github.com/capistrano/capistrano/issues/725#issuecomment-30089068
and there is also the git config way of doing it.
Merge pull request #63 from filipegiusti/master

Add the capistrano v3 way of using gateway servers
Merge pull request #58 from yagnik/master

added documentation to allow using capistrano from ruby script