ENH Add MultiIndex.from_product convenience function

FIX typo in from_iterables docstring

ENH Rename from_iterables to from_product

TST rework from_product test to compare against from_tuples

DOC Add notes on from_product to release notes and indexing docs

DOC clean from_product examples in docs

DOC Further clarify from_product docs
Merge pull request #6055 from mwaskom/multiindex_from_iterables

ENH Add MultiIndex.from_product convenience function