Fix typos and markdown issues on upgrading from 2.x.x page

- Fixed typo in one of headers
- Fixed spacing in one of list items
Merge pull request #34 from killthekitten/patch-1

Fix typos and markdown issues on upgrading from 2.x.x page
corresponding changes in sourcecode from previous commit
Fix a typo in faq.

inteactive -> inte**r**active
Merge pull request #35 from ouyoutouchmytralala/patch-1

Fix a typo in faq.
Fixed typo in release announcement
Merge pull request #36 from vredniy/patch-1

Fixed typo in release announcement
[✔] Fixed typos.
Don't advise users to use :all role
Shame on me. Of course, :all is a meta role:
https://github.com/capistrano/capistrano/issues/746
Capistrano v3 _is_ on rubygems.org
Merge pull request #40 from nathanvda/patch-1

Capistrano v3 _is_ on rubygems.org
Merge pull request #38 from kirs/fix-upgrade-guide

Don't advise users to use :all role
Merge pull request #37 from mkempe/typos

Fixed typos in release announcement.
Fix release announcement typos
Merge pull request #41 from aackerman/fix-typos

Fix release announcement typos
Removed manual to sign the gem
Fix spelling error "equivilent" -> "equivalent"
Merge pull request #43 from mitchlloyd/fix-spelling

Fix spelling error "equivilent" -> "equivalent"
Merge pull request #42 from kirs/fix-install-guide

Removed manual to sign the gem
Document role filtering.

Role filtering doesn't seem to be documented, and was added in a pull
request before v3 was released. This commit adds documentation for the
existing methods of setting the role filter, and how it works, as well
as the command line setting which is a pull request currently open.