New rules about favoring keywords unless/until over negations.

Favor unless (or control flow or) over if for negative conditions.
Favor until over while for negative conditions.
New rule: Use spaces around the = operator when assigning default values to method parameters
New rule: The new lambda literal syntax is preferred in Ruby 1.9.
Merge branch 'master' into more_rules
Merge pull request #27 from jonas054/more_rules

More rules