Improve the main page of the browser. Done for now.
Remove pure-HDF5 I/O code.

It works, but does not work any better than NetCDF-4. We can always
recover it later if we need to.
Stop trying to "import netCDF3".
Update calving command-line options. See #144.

Now we use -calving eigen_calving,thickness_calving,ocean_kill,float_kill

Option "eigen_calving" takes "-eigen_calving_K", as before.

Option "thickness_calving" takes "-thickness_calving_threshold" instead
of "-calving_at_thickness".

Option "ocean_kill" takes (and requires!) "-ocean_kill_file", which
specifies the name of the file with the ice thickness field used to
compute the maximum ice extent.

To combine several calving mechanisms, use a comma-separated list:

-calving eigen_calving,thickness_calving ...

Also tried the best I can to update all scripts in examples/, as well
as the User's Manual.