Switch from using object filters to using ASTs

*What*
Completely redoes the logic filter to use only parsed logic strings (as defined in https://github.com/phoebesimon/node-logic-filter-strings). This branch depends on https://github.com/phoebesimon/node-logic-filter-strings/pull/1 being merged/publish/installed.

*How*
index.js: Reworked the logic to assume that rules are added as strings and to operate on the value returned from parsing the string (an AST).
test/index.js: Got rid of object filter versions of tests

*Why*
The object filters would not let us specify a number of cases, most of which revolve around nested object, which it is essential to handle going forward.