add PlDoc examples for all_distinct/1, global_cardinality/2 and circuit/1
add PlDoc examples for all_distinct/1, global_cardinality/2 and circuit/1

jn7163/swipl-devel,mndrix/swipl-devel,mndrix/swipl-devel,jn7163/swipl-devel,edechter/swipl-devel,edechter/swipl-devel,mndrix/swipl-devel,jn7163/swipl-devel,koryonik/swipl-devel,edechter/swipl-devel,koryonik/swipl-devel,koryonik/swipl-devel,edechter/swipl-devel,koryonik/swipl-devel,mndrix/swipl-devel,jn7163/swipl-devel,koryonik/swipl-devel,jn7163/swipl-devel,mndrix/swipl-devel,edechter/swipl-devel