Boolean Search Operators.

Hi guys,
Please check carefully. I've changed a filter implementation. There are a lot of tests for old behaviour and for a new one. Seems I shouldn't break anything. 
@outcoldman I would like to improve generateExpressionTree function and in fututre for AND/OR logic create BST only once per search. I'll push this one in nearest future.
2) Now I've implemented AND operation with 'and' operator but we can change it of course.
3) Also whitespace should work now too.
Open for any comments