Write binary data to buffer
#include <buffer.h>
int buffer_putalign(buffer* b,const char* x,size_t len);
buffer_putalign is similar to buffer_put.
The difference to buffer_put is that, when there isn't enough space for new data, buffer_put calls buffer_flush before copying any data, while buffer_putalign fills all available space with data before calling buffer_flush.
0 if everything is fine, -1 on error (setting errno).