Add no-useless-length-check rule

[fisker]

Not finished yet, nested logic operators are complicated.

Fixes #897

[sindresorhus]

Suggested change

	'non-zero': '`Array#some()` returns `false` on empty array, the empty check is not needed.',
	zero: '`Array#every()` returns `true` on empty array, the non-empty check is not needed.'
	'non-zero': 'The empty check is useless as `Array#some()` returns `false` for an empty array.',
	zero: 'The non-empty check is useless as `Array#every()` returns `true` for an empty array.'

?

[fisker]

The message seems not right, I'll double-check the logic.

[fisker]

The message was wrong about the length check node, fixed.