Keep/Drop dice

Drops the specified number of lowest/highest dice.

Syntax
`dYdZ` `XdYdZ`	Drops the lowest Z dice from the result of `XdY`. Alias for `XdYdlZ`. May be used with `ns` and `!`.
`dYdlZ` `XdYdlZ`	Drops the lowest Z dice from the result of `XdY`. May be used with `ns` and `!`.
`dYdhZ` `XdYdhZ`	Drops the highest Z dice from the result of `XdY`. May be used with `ns` and `!`.
`dYkZ` `XdYkZ`	Keeps the highest Z dice from the result of `XdY`. Alias for `XdYkhZ`. May be used with `ns` and `!`.
`dYkZ` `XdYkZ`	Keeps the highest Z dice from the result of `XdY`. May be used with `ns` and `!`.
`dYklZ` `XdYklZ`	Keeps the lowest Z dice from the result of `XdY`. May be used with `ns` and `!`.
	None of these can be used with Critrange notation.