Scrapped conversion to object filter

*What*
After realizing that the object filter model was not going to be robust enough to describe all cases, I've elected to get rid of all the conversion functions and simply return the AST. This makes much more sense and we can even use the AST instead of object filter if we want

*How*
index.js: got rid of convert + helper functions; only return the parsed AST now
test/index.js: adjusted tests