add xxp utility

sh/xxp

@@ -0,0 +1,23 @@
+#!/usr/bin/env sh
+# YES_ZSH
+# YES_BASH
+# YES_DASH
+
+xxp() { ### @-
+    ### act like `xxd -p`, but nicely formatted.
+    ###
+    ### **TODO:** support `-r` (reverse) argument.
+    ###
+    ### ```
+    ### $ xxd -p ~/rc/install | head -n2
+    ### 23212f7573722f62696e2f656e762073680a232074686973207363726970
+    ### 7420697320636f6d70617469626c65207769746820666f6c6c6f77696e67
+    ### $ xxp ~/rc/install | head -n2
+    ### 23 21 2F 75 73 72 2F 62 69 6E 2F 65 6E 76 20 73
+    ### 68 0A 23 20 74 68 69 73 20 73 63 72 69 70 74 20
+    ### ```
+
+    hexdump -e '15 1 "%02X " 1 1 " %02X\n"' -- "$@"
+}
+
+[ "${SOURCING:-0}" -gt 0 ] || xxp "$@"