Add url checker

bin/util/urlcheck.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+# Check availability of external markdown links in the supplied document.
+
+# Github severely rate limits unless you use your access creds.
+github_secret=$(cat ../priv/github.txt)
+
+for x in $(grep -Pho '\(\Khttp[^)]+' $1 | sed 's/#.*$//g' | sort -u)
+do
+    echo $x;
+
+    # Include credentials for github.com
+    [[ "$x" =~ .*github.com* ]] && creds="-u $github_secret" || creds=""
+
+    # beaconcha.in doesn't like HEAD requests
+    [[ "$x" =~ .*beaconcha.in* ]] && head="" || head="--head"
+    
+    res=$(curl $creds -Lo /dev/null --silent $head --write-out '%{http_code}\n' $x)
+
+    if [ "200" -ne "$res" ]
+    then
+        echo "*** $res ***"
+    fi
+done