Rename C256Mgr into FoenixMgr

[vinz6751]

For historical reasons the scripts are named after the C256, and the messages in the script mention the C256.
Now that the scripts are used for all Foenix computers, not only the C256, it would make sense to rename this like "FoenixMgr" (suggestions welcome).

[daschewie]

You may want to consider closing this request and moving it to the https://github.com/pweingar/C256Mgr project. I know the utility is bundled with the kernel, but it is not part of it.

[pweingar]

There was a suggestion from someone earlier to rename the script "foenix," which seems pretty reasonable to me. And yes, this is more properly in the other repository. I'll make it an issue there.

[pweingar]

See: pweingar/FoenixMgr#5