Fixes in introspection and query methods

* Renamed .queryArray to .queryHash because it returns associative array
of objects as a hash
* Added .queryArray, it returns array of single values (not objects)
* Added Introspection method .indexes(tableName, callback)
* Changed Introspection method .tableInfo, now it returns object,
previously it was an array with single object, so we unwrapped it
* Changed Introspection method .fields, now it returns hash with field
name as a key
* Changed Introspection method .foreign, now it returns hash with
constraint name as a key