INT: followup to Index not a sub-class of ndarray

[jreback]

followup from #7891

• tests for argmin/argmax, DOC/TST: index followup #7951
• doc-strings for properties / functions that are ndarray compat, CLN/INT: remove Index as a sub-class of NDArray #7891, DOC/TST: index followup #7951
  • any/all doc-strings (series/index) (unbox already does this)
• searchsorted, WIP: searchsorted implementation #7447
• Index.__nonzero__ should raise ? bool(MultiIndex) seems to always return False #7897, fixed in DOC/TST: index followup #7951
• see if can figure out sortorder (e.g. in MultiIndex.repeat), leaving for now
• defined nbytes (for index its ok), for NDFrame this should actually return the memory of data + index memory (ENH: showing memory used #6852), done in CLN/INT: remove Index as a sub-class of NDArray #7891

[jreback]

closing, searchsorted is being address separately