NF: One/two-sided tests in permuted OLS (replace F-test with t-test)
permuted OLS: clean example (matplotlib colorbar stuffs)
Typos
Typos (2)
Permuted OLS: code coverage + associated bug fix + cosmit.
Permuted OLS: simplify example.

The minus sign is not removed in some of the figure ticks for which
it should be. However, the code is simpler by about five lines.
Permuted OLS: DOC: improve warning message.
Merge pull request #173 from VirgileFritsch/permuted_ols_tstat

NF: One/two-sided tests in permuted OLS (replace F-test with t-test)