unix/modos: Implement rename().
unix/modos: Implement rename().

rename() is considered a part of the baseline API, and should be builtin
to allow to write simple, but useful/reliable utilities.

Change-Id: Icd5ad9214a1453e97bbad5d4a4fad0951f8ccfb1
Signed-off-by: Paul Sokolovsky <9dc5061f178bb11813e14f1ed02ba27eaf21fa5d@users.sourceforge.net>

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython