NF: Add Massively Univariate Linear Model with permuted OLS.

An example is still needed and more tests may be welcomed.
cosmetic changes in permuted_ols + rename module.
Mass univariate: Add Haxby example.
Cosmit: move code around
MISC: refactor to remove code duplication
ENH: masking strategy for homogeneous background
ENH: better error message
ENH: integrate background mask heuristic
Integrate better new masking strategy
ENH: add slight smoothing to EPI mask extraction
Mass univariate -- permuted OLS: address PR comments.
permuted OLS: Correct doctests + C-contiguousity with copy()
Permuted OLS: fix contiguousarray problem (one check was missing).
permuted OLS: Modify example --> add thresholded F-score for comparison.
permuted OLS: adjust memory pre-allocation + robust sparsity threshold.
permuted OLS: add intercept by default + unit tests + code robustness.
BF: closes issue #162
ENH: cosmetic changes to testcase
BF: broken testcase
permuted OLS: backport for sklearn f_regression.