add base class for queries

Create Query classes that subsclass QueryBase and provide a `#as_hash`
method that constructs the hash to be passed on to the
`Elasticsearch::Client`. The subclass can also override the
`#parse_results` method to massage results into a format the application
expects to consume.
add query string sanitizer util
Change QueryBase class to Queryable mixin
change Document#model to Document#object
readme updates for queryable classes
Merge pull request #4 from ryanhouston/query-base

Create Queryable mixin for query classes