CLN: Remove unused ValuesProperty class.
DOC: add some missing entries to api docs
Merge pull request #5282 from jorisvandenbossche/docs-api-add1b

DOC: add some missing entries to api docs
Merge pull request #5276 from jtratner/remove-unused-ValuesProperty

CLN: Remove unused ValuesProperty class.
DOC: expand JSON docs
Merge pull request #5287 from Komnomnomnom/json-docs

DOC: expand JSON docs
ENH: Add array_equivalent, to address the handling of NaNs when comparing arrays for equality.

Added NDFrame.equals

Index, Float64Index, and MultiIndex's equal method now uses array_equivalent
instead of np.array_equal.
Goal: do not deteriorate performance by a factor of 7
Let Index use np.arary_equal by default.
Add a new method, `equivalent`, for handling NaNs.
Try using isnan
BUG: The change in array_equivalent makes it not work on object arrays.

To to salvage some usefulness in NDFrame.equals, we must loop to check
each column of the NDFrame separately.