Add tests for `query === undefined` pass-through.

The function shouldn't throw or return a destructive function if query
is undefined. This is a simple defensive approach.
Return the identity function if query is undefined

Tests now pass.
Add failing tests for a `deleteIgnored` option.

These are basically the same tests we use for `ignore`.
Add a `deleteIgnored` option.

If set to true, the ignored operators will be deleted from the query
object, while also not being used in the modifier.

Tests now pass.
Update and improve the documentation.

There were some typing mistakes and `options.deleteIgnored` needed to be
added.
Bump version to 0.2.0

This adds:
- An `deleteIgnored` option to delete the ignored operators from the
  query object
- Pass-through fix for when the query is undefined (if `query ===
  undefined` we stop and return the identity function)