added docs todo.
initial implementation of moment.

Also added tests. Currently the arguments `w` and `d` only do anything
when `cent`=True.
Merge branch 'master' of github.com:circstat/PyCircStat
now `moment` returns only the complex p-th moment

removed automatic return of magnitude and angle to make calling simpler.
implemented bootstrapping

Test function still needs work.
buggy push of decorators for moment

Do not merge back into main repo until fixed! This is a push so Fabi
can take a look.
Merge branch 'master' of https://github.com/tomwallis/PyCircStat