rebin filter transmission curves

[bd-j]

Some filter curves are at extremely high resolution. In some applications this might lead to speed issues, so one might wish to rebin (not interpolate!) the transmission curves to lower resolution. I guess a convolution could do this too.

anyway, a method to do this automatically given some desired output resolution might be helpful

[bd-j]

@jrleja here';s the issue for this idea, if you decide it would help

[bd-j]

@jrleja I wrote an observate.rebin() method in #22 to replace interpolations, but it could use some testing before being used in the Filter instantiations or the get_counts_x methods.

[bd-j]

Just noting this should also be the procedure when gridifying transmission curves, instead of interpolation onto the grid.