[Feature Request] Expose 'legal: false' option to public API moves() and move() function

[dhirallin]

I would like my interface to support several chess variants (slightly different rules).
This would be easy to implement if I were able to use moves() to obtain a list of all moves (legal and illegal) and then filter them down.
It would also be handy if I could make these pseudo-legal moves using move() and load() as well.
I noticed that your internal function _moves() already supports this, so I figure it should be doable to get it into the public API?
One example of a variant rule is that I want to be able to move a king into check and then perform subsequent moves without them failing.