ENH: Option to avoid "center" environment.
CLN: Improve warnings to avoid generic warnings messages

All generic Warnings have been replaced with specific warnings, which have
been consolidated into sm_exceptions.py.

Conflicts:
	statsmodels/tools/sm_exceptions.py
Added specific warnings in a couple of places where they were missing

Converted raise Warning to warning.warn

Made certain warnings had been imported in some modules where it was lazily
imported

Simplified warnings in GEE which was neither lazily imported nor imported
at the top of the file
Fix for conda 3.4 changes
Merge pull request #1510 from bashtage/warning-convert

CLN: Improve warnings to avoid generic warnings messages
Merge pull request #1544 from bashtage/travis-miniconda

MAINT: Fix travis miniconda build
Merge pull request #1438 from toobaz/uncentered_table

ENH: Option to avoid "center" environment.
COMPAT: Add NumpyVersion from scipy
Merge pull request #1432 from jseabold/fix-loose-version

COMPAT: Add NumpyVersion from scipy
MAINT: Deprecate rank in favor of np.linalg.matrix_rank
COMPAT: Add np.linalg.matrix_rank for <= 1.7.1
ENH: Use NumpyVersion for version testing
Merge pull request #1383 from jseabold/deprecate-rank

MAINT: Deprecate rank in favor of np.linalg.matrix_rank
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