ring_buffer actual capacity ?

[giltho]

Hello,

I think there is an issue with the ring buffer capacity. The buffer is allocated in the following way :

ringbuf->buf = rconf->mem_calloc(rconf->capacity, sizeof(Rbuf))

I am pretty sure it should be sizeof(uint64_t) instead. Right now, for a ring buffer of capacity 10, insteda of allocating 80 bytes, it allocates 640 bytes !
It is also possible to call rbuf_peek(rbuf, 79) on a ring buffer of capacity 10.

If I am right, I'll happily submit a PR to fix this