[En-Nut-Discussion] New function NutNvMemErase

[Thiago A. Corrêa]

Hi,

    It is quite common to have a default button to erase settings and
return them to default. When Nut/OS starts and the NV Memory is
uninitialized, it will load default settings, and so should user's
application code.

    I'm adding a missing functionality to NvMem functions to erase a
section of configuration, back to
it's uninitialized state. Specially for flash, where writes are
handled in full pages at a time, it's not possible to mimic this
functionality in application code without performing a lot of writes
and erases as it is with EEPROMs which can write individual bytes.

    So far, it's implemented for AVR 8 bits and AVR32. I hope others
can add implementations to their preferred platforms :)

Kind Regards,
    Thiago A. Correa