[Closes #144] Improve Capistrano integration docs.

 - Improve correspondance between the list of integration choices and the
   instructions below: links and terminology
 - Tighten documentation to make it clearer and faster to read.
 - Where possible, re-format Ruby code to avoid horizontal scrolling
Merge pull request #154 from rvm/144-broken_links_on_Capistrano_page

[Closes #144] Improve Capistrano integration docs.