Rewrite page(2) references to page(3).

Add description of new libmach.

man/man3/pipe.3

@@ -25,7 +25,7 @@ is available for reading from
 After the pipe has been established,
 cooperating processes
 created by subsequent
-.IR fork (2)
+.IR fork (3)
 calls may pass data through the
 pipe with
 .I read
@@ -41,7 +41,7 @@ when the read buffer is full or after reading the last byte
 of a write, whichever comes first.
 .PP
 The number of bytes available to a
-.IR read (2)
+.IR read (3)
 is reported
 in the
 .B Length
@@ -50,17 +50,17 @@ field returned by
 or
 .I dirfstat
 on a pipe (see
-.IR stat (2)).
+.IR stat (3)).
 .PP
 When all the data has been read from a pipe and the writer has closed the pipe or exited,
-.IR read (2)
+.IR read (3)
 will return 0 bytes.  Writes to a pipe with no reader will generate a note
 .BR "sys: write on closed pipe" .
 .SH SOURCE
 .B /sys/src/libc/9syscall
 .SH SEE ALSO
-.IR intro (2),
-.IR read (2),
+.IR intro (3),
+.IR read (3),
 .IR pipe (3)
 .SH DIAGNOSTICS
 Sets