can't setup initial fen without king

[snk-js]

Hi I need a slight parameter to setup the board without the king, for custom boards purposes, how can I achieve that?

Error: Invalid FEN: missing white king```

[jhlywa]

Illegal FEN is currently not supported. A temporary work-around would be to use .remove to remove the king after calling .load with valid FEN.

I may entertain the idea of adding a {strict: false} option to .load to bypass the FEN verification.

[snk-js]

Hey I made changes to fix this without breaking changes, added a test too, you can find the PR here #414

now we can bypass any rule than we want altogether within an array:

test('non-strict fen validation parameter (FEN with no kings)', () => {
  const noKingFen = '8/8/8/8/4R3/8/8/8 w - - 0 1'
  // chess: Chess(fen, config: { bypass: number[] }) -> Chess
  // strict is false will by bypass the 4th to 11th checks in validateFen

  // 1st criterion: 6 space-seperated fields?
  // 2nd criterion: move number field is a integer value > 0?
  // 3rd criterion: half move counter is an integer >= 0?
  // 4th criterion: 4th field is a valid e.p.-string?
  // 5th criterion: 3th field is a valid castle-string?
  // 6th criterion: 2nd field is "w" (white) or "b" (black)?
  // 7th criterion: 1st field contains 8 rows?
  // 8th criterion: every row is valid?
  // 9th criterion: is en-passant square legal?
  // 10th criterion: does chess position contain exact two kings?
  // 11th criterion: are any pawns on the first or eighth rows?

  const chess = new Chess(noKingFen, {
    // if not strict, we don't need to check the remaining criterions
    bypass: [4, 5, 6, 7, 8, 9, 10, 11],
  })
  expect(chess.fen()).toBe(noKingFen) // success
})

@jhlywa