Nobody ever used the return values anyway, so for reading just
return the string and for writing the number of bytes written

Doesn't need to be members, make standalone functions

Rename  to
read_lenPrefixed_uInt8s_ToO[U]String and
write_lenPrefixed_uInt8s_FromO[U]String, lengthy,
but much less unambiguous, seeing as a lot of users of it don't
seem to be aware that they read/write pascal-style length
prefixed strings, which isn't surprising given the
apparent simplicity of their original name.

added a unit test