ENH Addeded Fisher's method and Stouffer's Z-score method closes #3092
Refactor stats.combine_pvalues, add docs and tests

Refactored Fisher's method and Stouffer's method into a single method called
stats.combine_pvalues. Added documentation for this method, and added tests for
weighted Stouffer's method. Minor naming and style fixes.

Update THANKS.txt

Update autosummary

Use sf instead of 1 - cdf

Fix reST reference syntax

Coerce to ndarray, use more numpy functions

Add ref for test examples; test using python lists

Remove leftover text from git conflict

Add proper docstring format for list items
Merge pull request #3109 from cancan101/fisher_test

ENH Added Fisher's method and Stouffer's Z-score method