make str_t an opaque type. First char is always length.<p>1. If string is 0-15 chars long, str_t is a small string, aka char[16]. First byte is length, payload starts in 2nd byte, tail is always zeroed. Empty string is all zeros always.<p>2. If string is 16-248, str_t is a half string. The whole payload exist in a single contiguous buffer. First bytes is length. A pointer to the rest of the payload exist within the remaining 15 bytes, starting at the first alligned address. This way you can cast half string as small string when passing as value without knowing the size at compile time (and stil recover the rest of the payload). Gap between the length and the pointer is reserved and always zeroed.<p>3. For lengths 249 and higher. Each value 249-255 is not the lenght, but an encoded way to represent one or more styles of bigger strings. Not need to hold the payload in a single contiguous buffer. Remaining 15 bytes will hold a pointer to the data structure in the same fashion as half string. Reserved bytes are used to represent length if possible. If not, length is required to exist at a fixed position in the first buffer accesible when dereferencing the pointer.