Access to the gpxe.org and etherboot.org domains and associated
resources has been revoked by the registrant of the domain.  Work
around this problem by renaming project from gPXE to iPXE, and
updating URLs to match.

Also update README, LOG and COPYRIGHTS to remove obsolete information.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

The UEFI specification does not mention ROM checksums, and reassigns
the field typically used as a checksum byte.  The UEFI shell
"loadpcirom" utility does not verify ROM checksums, but it seems that
some UEFI BIOSes do.