Update period.py

proposed fix for #4699: Period() docstring inconsistent with code when freq has a mult != 1
DOC: added "Must be a singlular rule-code (e.g. 5T is not allowed)."
TST: allow to check for specific xlrd version and skip reader test if xlrd < 0.9
VIS: let scatter plots obey mpl color scheme (#3338)
BUG: Fix Index.__iadd__ bug by setting equal to __add__

fixes #4996

alias Index's __isub__ to __sub__

document fixes to #4996

index isub test

roll back everything non-iadd related
CI: use nose-show-skipped plugin to show skipped tests
CLN: remove print_skipped.py
CI: freeze the showskipped commit
DOC: minor release/v0.13 corrections
Merge pull request #5072 from cpcloud/travis-nose-skipped

CI/ENH: use nose-show-skipped plugin to show skipped tests
Add DatetimeIndex and Index documentation.

Start documentation for DatetimeIndex and Index.
 ENH: Ability to tz localize when index is implicility in tz

Fix to issue #4230 which allows to localize an index which is
implicitly in a tz (e.g., reading from a file) by passing infer_dst to
tz_localize.
Fix order of index methods
Merge pull request #5081 from jtratner/fix-order-of-index-methods

CLN: Fix order of index methods.
ENH: Added PySide support for qtpandas.
API: Enable changing the DataFrame in the DataFrameWidget.
DOC: Adding an example of using the DataFrameWidget.
EHN: Allow load_data to load the "Titanic" and other problematic R datasets
TST: Move tests from rpy/common.py to rpy/tests/test_common.py
TST: Add tests to demonstrate the enhancements made to rpy/common.py.
DOC: Add explanation to doc/source/release.rst and doc/source/v0.13.0.txt
BUG: fixed a bug in multi-level indexing with a Timestamp partial indexer (GH4294)
Merge pull request #5088 from jreback/mi_timestamp

BUG: fixed a bug in multi-level indexing with a Timestamp partial indexer (GH4294)