Added properly functioning case insensitive match without regex

pandas.core.strings.str_contains should now match case insensitivity properly if given regex=False and case=False.  Also added test cases for case insensitive pandas.core.strings.str_contains with and without regex.
Documentation for str_contains bug in changelog
ENH: allow read_excel to accept URLs (GH6809)
DOC: Use correct, non-deprecated arg name
TST: some yahoo options tests missing network decorator
Merge pull request #7549 from cpcloud/fix-network-error-yahoo-options

TST: some yahoo options tests missing network decorator
additional common.is_*_dtype tests in core.common
DOC: correct relase note
Merge pull request #7550 from sinhrks/rn_fix

DOC: correct relase note
Merge pull request #7545 from neirbowj/frame_to_excel_docstring

DOC: Use correct, non-deprecated arg name
Merge pull request #7531 from dsm054/excel-via-url

WIP/ENH: allow read_excel to accept URLs (GH6809)
BUG: Bug in setitem with list-of-lists and single vs mixed types (GH7551)
Merge pull request #7552 from jreback/iloc

BUG: Bug in setitem with list-of-lists and single vs mixed types (GH7551)
ENH: Adding a NotImplementedError for simultaneous use of nrows and chunksize.

For read_csv() the user intention most likely is to get a TextFileReader, when using the chunksize option, but simultaneous use of nrows is not implemented yet. This raises now a NotImplementedError. Test and entry to current whatsnew source (v0.14.1.txt) added.
Fixes #6774
BUG: DatetimeIndex.asobject raises ValueError when contains NaT
make better use of dtype tests in nanops
Merge pull request #7544 from sinhrks/dtmixin

BUG: DatetimeIndex.asobject raises ValueError when contains NaT
PERF: vbench for mixed groupby with datetime (GH7555)

PERF: perform coercing and casting on groupby agg by blocks
Merge pull request #7085 from michaelaye/add_notimp_error

adding a NotImplementedError for simultaneous use of nrows and chunksize...
Merge pull request #7560 from jreback/groupby_first_perf

PERF: vbench for mixed groupby with datetime (GH7555)