Liquid UTF-8 support

Adds support for UTF-8 word characters in Ruby 1.9 that is also backwards compatible with 1.8 from #164

**Before:**
```ruby
@template = Liquid::Template.parse("hi {{ordem_número}}")
@template.render( 'ordem_número' => '201300000000017' )
=> "hi "
```

**After:**
```ruby
@template = Liquid::Template.parse("hi {{ordem_número}}")
@template.render( 'ordem_número' => '201300000000017' )
=> "hi 201300000000017"
```


@boourns & @Soleone & @dylanahsmith for review