Add Write.buffer() reset method

The new method allows reusing the buffer instance to generate multiple
messages in a loop.

Author: elprans

buffer.pxd

@@ -34,6 +34,7 @@ cdef class WriteBuffer:
     cdef inline _check_readonly(self)
     cdef inline _ensure_alloced(self, ssize_t extra_length)
     cdef _reallocate(self, ssize_t new_size)
+    cdef inline reset(self)
     cdef inline start_message(self, char type)
     cdef inline end_message(self)
     cdef write_buffer(self, WriteBuffer buf)

buffer.pyx

@@ -113,6 +113,10 @@ cdef class WriteBuffer:
         hton.pack_int32(&self._buf[1], <int32_t>mlen)
         return self
 
+    cdef inline reset(self):
+        self._length = 0
+        self._message_mode = 0
+
     cdef write_buffer(self, WriteBuffer buf):
         self._check_readonly()