+ cosmetic changes

Improved and simplified writers not needing specific BindSupport
(contrary to DataWriter)
Replaced QBindTable with optional Val::meta(...) to support Cbor tags,
Xml attributes, and even N-dimensional structures like
QStandardModelItem that support tables, arrays and trees

Made Cbor performance close to the minimum with well-formedness
guarantees using putBigEndian similar to QDataStream and
std::vector<bool> (no malloc until deep levels)
Made QWritable costless with std::function
Made QWritable flexible with QWritable<Writer> + IWriter
Added IWriter for even simpler implementations
WIP: Added QVariant and table experiments