Rename zentry->slice. Update some doxygen comments.

pub/lib/CMakeLists.txt

pub/lib/Doxyfile

pub/lib/axis.cpp

pub/lib/axis.hpp

pub/lib/coord.cpp

pub/lib/coord.hpp

pub/lib/curve.cpp

pub/lib/dualplot.cpp

pub/lib/edif.cpp

pub/lib/expr.cpp

pub/lib/expr.hpp

pub/lib/file_in.cpp

pub/lib/file_out.cpp

pub/lib/fit.cpp

pub/lib/import.cpp

pub/lib/manip.cpp

pub/lib/node.cpp

pub/lib/olf.cpp

pub/lib/olf.hpp

pub/lib/opr.cpp