Add support for limit in zrangebylex

Initial request was a [twitter conversation](https://twitter.com/ayrtonbe/status/494103060860633088).

Anything else I missed?
Done

On 01 Aug 2014, at 12:11, Ryan Biesemeyer <notifications@github.com> wrote:

> In test/commands_on_sorted_sets_test.rb:
> 
> > @@ -8,6 +8,17 @@ class TestCommandsOnSortedSets < Test::Unit::TestCase
> >    include Helper::Client
> >    include Lint::SortedSets
> >  
> > +  def test_zrangebylex
> > +    r.zadd "foo", 0, "aaren"
> > +    r.zadd "foo", 0, "aarika"
> > +    r.zadd "foo", 0, "abagael"
> > +    r.zadd "foo", 0, "abby"
> > +
> > +    assert_equal ["aaren", "aarika", "abagael", "abby"], r.zrangebylex("foo", "[a", "[a\xff")
> > +    assert_equal ["aaren", "aarika"], r.zrangebylex("foo", "[a", "[a\xff", :limit => [0, 2])
> > +    assert_equal [], r.zrangebylex("foo", "(aaren", "(aaren\xff")
> looks good so far. could you add a variant on the ( prefixes that matches at least one item?
> 
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