add string implementation, can handle partial string slices

finish core implementation, added Index object

fix up the logic

add in new SliceOption object, cleaning up tests

python part of random ops

added random select sub policy

validators added

comments added, remaining issues addressed

add more python test cases

fix ci

fix CI

fix order of include files

addr review cmts

addr review cmts

reorg file

fix compile err

address review cmts

address review cmts