Caching Trie data structure

Hi,

I faced an issue with caching internal search index structure inside `localStorage`. The problem is, when you change tokenized fields, nothing really happens — old structure is used and you need to manually clear `localStorage`.

So, it's not too critical, but I spent several hours to understand what's happening.

Perhaps it would be better to put the trie structure in `sessionStorage` or somehow mark this thing in the documentation.