Use "tags" as base field rather than "tags_array"

@lgs I did some refactoring so that the underlying Mongoid field is now called "tags" (type Array) rather than "tags_array". I think this is more natural/clean because you can just call "tags" directly without any magic/conversion needed in the gem, however, it does have potential to break existing code hence I bumped the version to '1.0.0' according to semver.

All tests passing and code has been synced to your latest commit.

It's your call whether to merge it or not, either way I'm fine :beers: