ENH: Medcouple for robust skewness estimation
ENH: Function allowing other functions to be applied using only 1d
    at a time
ENH: Robust Skewness from Kim and White
ENH: Robust Kurtosis from Kim and White
ENH: Helper functions for quantile.  Different from numpy.
ENH: Tests for medcouple
BUG: Made use of np.apply_along_axis and replaced custom version
General improvements to robust skewness and kurtosis
ENH: Generalized other texts to work along axis for standards
Simplified code to remove new weighted quantile function, instead
    use np.percentile
Removed incorrect test file in tools/tests/test_statstools.py
Added tests for multi-axis functions in stattools
Clean-up and documentation for robust skewness and kurtosis measures
Cleaned-up stattools
Added docstring for those missing
Added test for robust kurtosis
Fixed defect where ties were not handled correctly by medcouple
Reverted space additions around ** operator
Removed unnecessary float powers
100% test coverage

Conflicts:
	statsmodels/stats/tests/test_statstools.py
Revert auto-spacing
ENH: Added flag to select excess or not
Allows raw values to be returned when excess=False

Conflicts:
	statsmodels/stats/stattools.py
Added test for excess=False case

Conflicts:
	statsmodels/stats/tests/test_statstools.py
Vectorized np.percentil use
Switched to vectorized use of np.percentile where appropriate
Cleaned up some excessively verbose code

Conflicts:
	statsmodels/stats/stattools.py
Documentation improvements and additional options
Added math to robust_kurtosis
Added math to robust_skewness
Made some of the parameters in robust_kurtosis settable
Added tests of new features

Conflicts:
	statsmodels/stats/stattools.py
Improved documentation of robust kurtosis
Separated the expected kurtotis calculation

Conflicts:
	statsmodels/stats/stattools.py
Added a release note.
Fixed rebase issues
Fixed spacing with **
Merge pull request #1234 from bashtage/medcouple

ENH: Robust skewness, kurtosis and medcouple measures
ENH: Unit Root Tests

Introduces 4 new unit root tests and provides a class for Augmented Dickey Fuller testing.
The four new tests are:
  - PhillipsPerron
  - KPSS
  - Variance Ratio
  - DF-GLS

These have all been included in unitroot.py, and the afduller function has been moved from
tsatools to unitroot, and is now just a wrapper around the ADF class.

The critical value and p-value lookup codes have also been consolidated into untiroot.py.
Critical value and p-value lookup information for DFGLS and KPSS is not readily available
in published form, and so simulations were performed to generate these using 100,000,000
replications using a methodology similar to MacKinnon (2010).  All critical value data
has been consolidated into tsa/critical_values.

A cov_nw function was added to tsa/stattools which computes Newey-West covariance.

Also includes substantial improvements to tsatools, including numerous bug fixes.   The
code that handled recarrays has been improved to now handle pandas dataframes.  Numerous
doc strings where improved.  Test coverage was also substantially increased.

string_types was added to the compatibility library to address the difference between basestring
in Python 2 and str in Python 3.

Moved coint to a new file coinegration.py which will, in the long term, be expanded to include
other tests for cointegration.

Conflicts:
	statsmodels/tsa/tsatools.py
Changed h0 and hA to null_hypothesis and alternative_hypothesis

Provides a __str__ and __repr__, as well as a _repr_html_ for IPython, for unit
root tests to improve interactive behavior

Refactored valid_trends to remove redundant code