Removed checks in Pfx.Validate for prefixes that could be
misinterpreted as callsigns. These checks were included because of a
misunderstanding of what the Pfx field contains.
Updated the user manual to remove the description of these checks from
the Pfx entry in the QSO Fields and Validation table.
This completes changes for issue #127.
Also updated the Call entry in the same table to remove
description related to future changes to HamQSLer as these changes
were made as part of issue #122.