ENH: add Index.is_monotonic_decreasing and Index.is_monotonic_increasing

Index.is_monotonic will have a performance degradation (still O(n) time) in
cases where the Index is decreasing monotonic. If necessary, we could work
around this, but I think we can probably get away with this because the fall-
back options are much slower and in many cases (e.g., for slice indexing) the
next thing we'll want to know is if it's decreasing monotonic, anyways.

see GH7860
ENH: support monotonic decreasing indexes in Index.slice_locs

also: NaN and NaT imply not monotonic
ENH/BUG: support Categorical in to_panel reshaping (GH8704)
CLN: move block2d_to_blocknd support code to core/internal.py
TST/BUG: support Categorical reshaping via .unstack
Merge pull request #8705 from jreback/to_panel

ENH/BUG: support Categorical in to_panel reshaping (GH8704)
Merge pull request #8680 from shoyer/reversed-monotonic-slices

ENH: slicing with decreasing monotonic indexes
BUG: Fix pandas.io.data.Options for change in format of Yahoo Option page

ENH: Automatically choose next expiry if expiry date isn't valid

COMPAT: Remove dictionary comprehension to pass 2.6 test

BUG: Add check that tables were downloaded.

ENH: Replace third_saturday function with Pandas offset

BUG: Check to make sure enough option tables are downloaded.

TST: Add sample options page during market open.

DOC: Add bug fix report to v0.15.1.txt for data.Options

BUG: Ensure that the value used for chopping is within the range of strikes.

TST: Add test for requesting out of range chop

BUG: Fix missing underlying price and quote time in first process data

BUG: Fix AM/PM on quote time

ENH: Refactor to expose available expiry dates

DOC: Update documentation for Options given Yahoo change.

DOC: Update documentation for Options given Yahoo change.

BUG: Undo accidental deletion of privat emethods

ENH: Add ability to use list as expiry parameter.

Also has year & month return all data for the specified year and month.

TST: Remove tests for warnings that are no longer in use.

DOC: Update docstrings of Options class.
DOC: Update docstrings of Options class.

Add documentation of month and year in remote_data.rst
ERR: leftover from renaming outtype to orient in to_dict
DOC: Select row with maximum value from each group
Merge pull request #8724 from unutbu/groupmax-recipe

DOC: Select row with maximum value from each group
COMPAT: Compat issue is DataFrame.dtypes when options.mode.use_inf_as_null is True (GH8722)
Merge pull request #8726 from jreback/inf

COMPAT: Compat issue is DataFrame.dtypes when options.mode.use_inf_as_null is True (GH8722)
Merge pull request #8721 from jorisvandenbossche/to_dict-invalid-orient

ERR: leftover from renaming outtype to orient in to_dict
Merge pull request #8631 from dstephens99/issue8612

BUG: Fix pandas.io.data.Options for change in format of Yahoo Option page
VIS: register datetime64 in matplotlib units registry (GH8614)
Merge pull request #8693 from jorisvandenbossche/plot-datetime64

VIS: register datetime64 in matplotlib units registry (GH8614)
CLN: fix conflict leftovers
ENH: read_csv dialect parameter can take a string (GH8703)
BUG: Bug in slicing a multi-index level with an empty-list (GH8737)
ENH: DataReaders return missing data as NaN rather than warn.

Fixes #8433