Set search ivar and pass params explicitly.
Move sorts instantiation to constructor in order

to maintain thread safety and prevent a potential race condition from
memoization.

Before this commit, freezing the search object ivar in the SortLink
class to verify that it is not being mutated was raising errors due to
this.

@ernie, @radar, let me know if this isn’t a good idea.
Remove #with_indifferent_access methods.

Tests pass without them despite using both symbol and string keys.
Maybe I’m missing something here. Let’s see what travis-ci says for the
older Rubies/Rails.