Scrapped conversion to object filter

index.js: got rid of convert + helper functions; only return the parsed AST now
test/index.js: adjusted tests
Updated README to show the correct output of inputting a string to logicFilterString
Merge pull request #1 from phoebesimon/phoebesimon/scrap-conversion-to-json-object-filters

Scrapped conversion to object filter
Remove all DeMorgans' translation logic, since it's no longer necessary

parser.js: removed DeMorgan's translation logic
test/*.js: removed/updated DeMorgan's tests