keyboard.h: add some missing key enums from Plan 9

Change-Id: I0d8b94037309b15f839588c6547acaaaf3e2ed4d
Reviewed-on: https://plan9port-review.googlesource.com/1151
Reviewed-by: Russ Cox <rsc@google.com>

include/keyboard.h

diff --git a/include/keyboard.h b/include/keyboard.h
index a3d02d0..0fe077a 100644
--- a/include/keyboard.h
+++ b/include/keyboard.h
@@ -33,7 +33,12 @@
 	Kalt=		KF|0x15,
 	Kshift=	KF|0x16,
 	Kctl=		KF|0x17,
-	
+
+	Kbs=	0x08,
+	Kdel=	0x7f,
+	Kesc=	0x1b,
+	Keof=	0x04,
+
 	Kcmd=	0xF100	/* Rune: beginning of Cmd+'a', Cmd+'A', etc on Mac */
 };