Closes issue #2

Makes compatible with ActiveRecord 3.2
Fixup rvm nonsense
Add rake as a dependency
Remove yarddoc
Version bump to 0.1.0
Regenerate gemspec for version 0.1.0
Add tagged_similar and tagged_with_scored
experiments with arel
Introduce tagged_with_tags_count

For example


	Photos.tagged_with(["funny", "naughty", "green"]).where{tags_count >= 2}

is the same as

	Photos.tagged_with(["funny", "naughty", "green"], :min => 2)

but more complex queries can be chained with the new first form. As
well the inner part of the query which contains group and
aggregate function is shielded from ActiveRelation so that
you can chain further aggregate functions if you wish in
an intuitive way.
Version bump to 0.2.0
Regenerate gemspec for version 0.2.0
Updated to show how to use the tags_count column
Get tagged_similar working and spec'd
Don't add in the instance methods unless required
Version bump to 0.3.0
Eliminate contexts for tagged_similar that have no tags
Update doc to reflect tagged_similar changes
Version bump to 0.3.1
Regenerate gemspec for version 0.3.1
Update readme to format nice on Github