Enhanced Ruby do blocks

Not all Ruby 'do' blocks take a variable, so, let's provide the option.

I've remapped the existing 'do' block to "doo", which would result in the following:

<pre><code>do |cursor_is_here|
  
end</code></pre>

Whereas now "do" is maps to this snippet:

<pre><code>do#cursor is here
  # subsequent tab puts cursor here
end</code></pre>