Updated pspec_pipeline/pspec_chans.sh

 - added polarizations to the directory structure
 - allowed for other separations than just E,NE,SE
 - renamed pspec_pipeline/pspec_chans.sh -> pspec_pipeline/mk_pspec.sh
 - added build to .gitignore so we don't have to worry about annoying messages.

 TODO:
 - What happens when we request more jobs than available threads?
 - Can we redesign this so we can pass options and not have to modify the
        script for each use?