Bugs and enhancements in weightstats

full test coverage now 98% verified, but not all options

fixed a few bugs, added some options
added TOST
added power for t_tests, plus basic framework for root finding
added power and enhancements for chisquare gof
added confint_proportion  for binomial porportion     function name ?
added power classes for normal (proportion) and chisquare
added power for F-test (problems: precision only 6 decimals (scipy ncf?), rootfinding for effect size see c6320d0)


still missing:

edit docstrings
check interface, function/method arguments
nice printing of test results, 
maybe: return distribution instance
compare ttest with ANOVA and OLS/WLS

check what goes in stats.api.py and submodules 
    public access to function in ``_proportions.py`` ?  lower level than stat.api ?

*power*
some additional comments, todos in module docstring of power.py
make sure tests cover the full range of values. If effectsize then bugs can look like precision issues.

not checked: compare and tests when data is 2d, might require 1d in CompareMeans

should we merge paired and independent ttests, same for tost ?

need examples for usage, especially definitions of effectsize as they are used in the power functions.

Refactor (todo):  
one-sided to greater/smaller DONE
ttest solve_power: doesn't have df argument (cannot be None), 
   (needed for power with dof Satterthwaite, won't directly work, dof_satt needs nobs, leave for later)

naming inconsistency: 
dof or df ?

future enhancements:
The power calculations, e.g. for sample size, can be improved by explicit solutions when they exist.