update url for hsb2 dataset
ENH: tools brentq_expanding, initial version
TST: add test asserts
REF: cleanup, remove unnecessary variables
DOC/TST: docstring, check case with start_low/start_upp arguments
TST: testing some exceptions,  incorrect input, and maxiter
DOC: notes
ENH: more options and full_output
ENH: some checking for NaNs,
     should work now if func is only defined for positive arguments
ENH: power use brentq_expand as rootfinder (tested with next commit)
ENH: try to get around symmetry of effectsize around zero for F-distribution
REF: power: enable old solver version as backup
REF/DOC: rename cache_fit_res, update docstring notes
REF: power solve, add success status to cach_fit_res, add UserWarning
BUG/TST: solve_power: fix one success code, tests for failing cases
TST: proper handling of warning, requires python >= 2.6
REF: cleanup and adjusting some conditions in brentq_expanding
REF: rootfinding, move test and example out of module
REF rootfindig: fix tests and examples after move, raise one more case
Merge pull request #723 from josef-pkt/root

Rootfinding for Power calculations