Adds Debian 10 (buster) and bullseye testing

Closes https://github.com/antonym/netboot.xyz/issues/339

src/debian.ipxe

@@ -11,11 +11,11 @@ clear debian_version
 clear older_release
 menu ${os} - ${arch_a} - Image Sig Checks: [${img_sigs_enabled}]
 item --gap Latest Releases
+item buster ${space} ${os} 10.0 (buster)
 item stretch ${space} ${os} 9.0 (stretch)
 item jessie ${space} ${os} 8.0 (jessie)
-item wheezy ${space} ${os} 7.0 (wheezy)
 item --gap Testing Releases
-item buster ${space} ${os} buster (testing)
+item bullseye ${space} ${os} bullseye (testing)
 item sid ${space} ${os} sid (unstable) 
 item --gap Older Releases
 item older_release ${space} Set release codename...