#8 tu does not change unit of E0

[sebastian_busch]

when doing tu on the data, x and y are changed nicely
(for example from meV to ueV). However, E0 remains in
meV, giving an error when doing _coq: Starting the
energy range at -10 starts at -10 ueV. However, giving
-10'000 (in order to have a curve starting at -10meV)
throws an error, stating that there are no data at
-10'000 _meV_. one has to adjust it manually via er.