planetarium: Create an (r3rs) package and use it.

planetarium: Create an (r3rs) package and use it.

Fix planetarium.pkg.  Putting files into separate packages requires
some changes.  Move read-cil-file to an MIT-Scheme-specific
package/file; move cil-file to load before mit-scheme-cil.scm.  Add
explicit clear-graphics and flush-graphics exports from the graphics
packages.  Why did geometry.scm have to be changed?