Add the concept of a "console usage", such as "standard output" or
"debug messages".  Allow usages to be associated with each console
independently.  For example, to send debugging output via the serial
port, while preventing it from appearing on the local console:

  #define CONSOLE_SERIAL CONSOLE_USAGE_ALL
  #define CONSOLE_PCBIOS ( CONSOLE_USAGE_ALL & ~CONSOLE_USAGE_DEBUG )

If no usages are explicitly specified, then a default set of usages
will be applied.  For example:

  #define CONSOLE_SERIAL

will have the same affect as

  #define CONSOLE_SERIAL CONSOLE_USAGE_ALL

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

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

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resources has been revoked by the registrant of the domain.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>