Add chan_send_(int|double|buf), chan_recv_(int|double|buf).

Related issue #7 

Sorry I'm not native specker. I may add mis-spelling or broken phrase. So I didn't write comment.
Should probably check if `wrapped == NULL` just to be completely safe.

```c
int* wrapped = malloc(sizeof(int));
if (!wrapped)
{
    errno = ENOMEM;
    return -1;
}
```