Update the Ruby version to 1.9.3-p392 also in tests
add examples of installing rubies with ruby-build

One of the things I miss from rbfu is the copy and pasteable ruby-build instructions on the main page.
fix broken directory paths

I copied and pasted those examples from the rbfu page, like an idiot.
alternatives that have deprecated noted as such
Merge pull request #109 from havenwood/upstream

alternatives that have deprecated noted as such
add details for installing to /opt/rubies

Also, rubyies should be prefixed with ruby-
change ruby-build instructions to match setup.sh

use ruby-1.9.3-p392, jruby-1.7.2 and rubinius-2.0.0-rc1 to match scripts/setup.sh
Merge pull request #108 from AndrewVos/master

Add examples of using ruby-build to install some rubies
Reorganized the Rubies section.
correct dir name for ruby-build 1.9.3 example
Merge pull request #110 from skorfmann/patch-1

correct dir name for ruby-build 1.9.3 example
Fix ruby-build stuff in README

They changed the names to remove ruby as a prefix.
Merge pull request #111 from steveklabnik/patch-1

Fix ruby-build stuff in README
/opt/rubies/ directories should be of the form "name-version".
Advocate using /opt/rubies/
Preserve the existing GEM_PATH before prepending to it.
Also include the CHRUBY_VERSION in the bug report.
Update the ChangeLog for 0.3.4.
Update the versions.
Update the chruby versions in the README.