Custom world generation/processor


 * The root tag
 * : A list of processors
 * : Can be or
 * If is :
 * : A number between 0 and 1
 * If is :
 * : A list of rules to apply from top to bottom
 * : The predicates to apply to the block's position, see below for a list of valid predicates
 * : The predicates to apply to the block that is placed
 * : The predicates to apply to the block before the structure is generated
 * : The block that is placed if all conditions are met
 * : ID of the block
 * : Block states
 * : A block state key and its value
 * : Block states
 * : A block state key and its value