input/protocoldata: also accept comma separated data values

Frame format specs in the header section accepted space and comma
separators already (though comma separated frame format details are
considered unusual). Protocol values in non-comment (text mode) lines
assumed strictly space separated fields.

Accept comma and semicolon too as data value separators for maximum user
convenience. Simplifies the import of post processed other text formats,
only requires the addition of headers and decoration (select control,
text to number conversion base), but allows re-use of all existing
values. Reduces diffs before and after manipulating original text into
protocoldata which sigrok can import.

These separators silently get ignored. They don't have a meaning in the
sense of interpreting "1, , 3" as three values. There is no concept of
empty fields in the sequence of data values. This is pure convenience.