CLN: consolidate Iterator interface

[jreback]

In several of the IO interfaces, we allow chunksize= and iterator to allow chunk reading. These all use sepearate non-conforming base classes.

We should create a base class core/base.py/Iterator that inherits from collections.Iterator. Then incorporate as much of this combined functionaility into this base class. To have them each have a similar interface.

• read_stata ENH Read Stata dta file incrementally #9493, Iterableiterator #12173
• read_hdf here
• read_csv Iterableiterator #12173
• read_msgpack here

[mroeschke]

Going to mention iterators as a point to consolidate in #15008. Going to close this one in favor of that one