Implement new zserio type 'bytes'

[mikir]

Currently, if there is a need to model array of bytes, it is possible to use zserio array of uint8:

struct BytesArray
{
    uint8 bytesArray[];
};

However, such construct has the mapping to the native languages which does not have to be optimal for users:

• C++: std::vector<uint8_t>
• Java: short[]
• Python: typing.List[int]

For example, Java users might want special mapping to byte[] and Python users might want special mapping to bytearray. In another words, users might want zserio type which just mean some array of bytes not array of numbers. This might be useful, e.g. for images. Therefore, we suggest to implement new zserio type bytes.

Comparing to current extern zserio type, new zserio type bytes will store number of bytes (not bits) as a varsize before array during serialization. This could potentially save some bits because varsize can encode small values more efficiently.

Mapping will be as follows:

• C++: std::vector<uint8_t>
• Java: byte[]
• Python: bytearray