Comments seismic

OMG... this is my first pull request.
And I gave up on the equation for attenuation correction in the docs, I couldn't get that to work.
Also, I made some unimplemented functions private, so they wouldn't show up in the doc, but there might be a better way of doing that.
There is no "file" or file format specified for RadiusTable. If you derive from RadiusTable you need to fill the arrays table_*. How you do it is up to you.