src/write_buffer.h: Use struct lsh_queue.

* src/write_buffer.h (write_buffer->length): New instance
variable.

* src/write_buffer.c (write_buffer_consume): New function.

Rev: src/resource.c:1.5
Rev: src/resource.h:1.5
Rev: src/write_buffer.c:1.15
Rev: src/write_buffer.h:1.14