gcc 15 and C23 force some union trickery on buffer.h :-(

add a few buffer_init*_forread variants to pretend we have type safety
  make sure buffer_init_staticcontents handles flushing attempts

buffer/buffer_init_read.3

@@ -0,0 +1,32 @@
+.TH buffer_init_read 3
+.SH NAME
+buffer_init_read \- initialize buffer structure
+.SH SYNTAX
+.B #include <libowfat/buffer.h>
+
+void \fBbuffer_init_read\fR(buffer &\fIb\fR,
+                int \fIfd\fR, char* \fIy\fR, size_t \fIylen\fR);
+
+.SH DESCRIPTION
+buffer_init_read is equivalent to calling buffer_init_forread with read(2) as op.
+
+.SH EXAMPLE
+  #include <libowfat/buffer.h>
+  #include <libowfat/open.h>
+
+  char buf[4096];
+  int fd=open_read("/etc/services");
+  buffer input;
+
+  if (fd>=0) {
+    char x;
+    buffer_init_read(&input,fd,buf,sizeof buf);
+    while (buffer_get(&input,&x,1)==1) {
+      buffer_put(buffer_1,&x,1);
+      if (x=='\\n') break;
+    }
+    buffer_flush(buffer_1);
+  }
+
+.SH "SEE ALSO"
+buffer_init(3), buffer(3), buffer_init_write(3)