Label *.nin *.pin as binary in git, tag as hex for diff

This allows the .git/config to have an entry like:

[diff hex]
  textconv = hexdump -v -C
  binary = true

.gitattributes

@@ -0,0 +1,3 @@
+# Binary files (no line-ending conversions)
+*.pin binary diff=hex
+*.nin binary diff=hex