[File] [PATCH] Recognize Varvara Uxn ROMs with metadata

[Samuel Dionne-Riel]

It might be possible with heuristics to recognize ROMs without
metadata, but I suppose it would be hard, as it's pretty much raw binary
data without common structure, other than things like JSRs paired with
JMP2r.

Verified with:

```
 $ file -m $repo/magic/Magdir .../*.rom
.../uxndis.rom:   Varvara Uxn ROM with metadata at 0x3bd (Uxndis)
.../meta.rom:     Varvara Uxn ROM with metadata at 0x139 (Meta)
.../notepad.rom:  Varvara Uxn ROM with metadata at 0x14b (Note Pad)
```

Signed-off-by: Samuel Dionne-Riel <samuel at dionne-riel.com>
---
 magic/Magdir/uxn | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
 create mode 100644 magic/Magdir/uxn

diff --git a/magic/Magdir/uxn b/magic/Magdir/uxn
new file mode 100644
index 00000000..3f2522e7
--- /dev/null
+++ b/magic/Magdir/uxn
@@ -0,0 +1,16 @@
+#------------------------------------------------------------------------------
+# uxn:  file(1) magic for Uxn ROM files
+#
+# https://100r.co/site/uxn.html
+# https://wiki.xxiivv.com/site/uxn.html
+#
+# Created by Samuel Dionne-Riel <samuel at dionne-riel.com>
+
+# https://wiki.xxiivv.com/site/metadata.html
+0x00 byte =0xa0
+>0x01 ubeshort x
+>>0x03 byte =0x80
+>>>0x04 byte =0x06
+>>>>0x05 byte =0x37           Varvara Uxn ROM
+>>>>>0x01 ubeshort x          with metadata at 0x%x
+>>>>>>(0x01.S-0x0ff) string x (%s)
-- 
2.44.1