Fix to cope with @CO records; they don't need to be key:value pairs.
Removed defunct MAX_NAME_LEN macro
Added cope to cope with "*" as the sequence.
Added support for header containers with container length larger than
the enclosed blocks (an unused device at present).

When writing SAM header containers we now also pad out the string with
additional nul bytes to permit in-situ editing.
Removed various clang and newer gcc compiler warnings.