Introduce libbuf analogous to toybuf but for use by lib/*.c. Change readfile() semantics to be able to read into an existing buffer, or malloc its own if that's NULL.
diff --git a/toys.h b/toys.h
index c810123..b7acc27 100644
--- a/toys.h
+++ b/toys.h
@@ -113,9 +113,9 @@
jmp_buf *rebound; // longjmp here instead of exit when do_rebound set
} toys;
-// One big temporary buffer, for use by commands (not library functions).
+// Two big temporary buffers: one for use by commands, one for library functions
-extern char toybuf[4096];
+extern char toybuf[4096], libbuf[4096];
extern char **environ;