periodicMask has wrong parameter

the lib function saqc.lib.tools.periodicMask has a param called include_bounds.

as the docstr mentions, its purpose is to include or exclude the boundaries. But, instead, it inverts the whole mask.

i remember, once we had both options, include/exclude and inverting, but at some point we throw one out (i assume it was the inversion, because one simply can invert the result by ~result).

Be that as it may, currently neither is correctly implemented.

@luenensc : can you have a look and decide which you think is the desired option ?