Method 'nelect_window()' now correctly takes into account a subset
of bands selected by the energy window.
Also, the number of electrons is now output to a '*.grX' file.
Added a check to 'check_data_consistency()' that verifies
that each shell contains only one sort of ions.
Also added a non-functioning test (implementation is commented)
for the function.
It requires a full set of VASP files for an example with multiple atom sorts.
The names of the test suites have been prefixed with an underscore
to avoid name conflicts with corresponding modules.
Also an attempt to make a scan of all tests has been made by
creating a 'test_all.py' script that is supposed to discover all
test cases and run them. Unfortunately, this does not work as expected
because many tests use input files assumed to be found in the current
directory, which is not true if the tests are run from a different
(parent) directory.
This can be fixed by either forcing the change of directory (but it
seems that 'unittest' does not have this functionality) or
prepending input file names with the current module directory.
