Forms a new spectrum, with each channel formed by an average over N channels of
the original. Binning starts in the first channel of each unmasked sector, and
proceeds until too few channels are left for a complete bin. The unused
channels are abandoned, and the sector centre frequency etc.are modified as
appropriate. BIN-SPECTRUM is equivalent to a boxcar average over N channels,
followed by copy of every 
channel into a new spectrum, with resolution
bandwidth N times that of the original.
Examples:
>> bin-spectrum<CR>
Bin width? (channels) [ 1] 2<CR>
..
