Fix a bunch of broken internal links in the docs. Add a hokey link checker.

src/etc/check-links.pl

@@ -0,0 +1,26 @@
+#!/usr/bin/perl -w
+
+my $file = $ARGV[0];
+
+my @lines = <>;
+
+my $anchors = {};
+
+my $i = 0;
+foreach $line (@lines) {
+    $i++;
+    if ($line =~ m/id="([^"]+)"/) { 
+        $anchors->{$1} = $i;
+    }
+}
+
+$i = 0;
+foreach $line (@lines) {
+    $i++;
+    while ($line =~ m/href="#([^"]+)"/g) { 
+        if (! exists($anchors->{$1})) {
+            print "$file:$i: $1 referenced\n";
+        }
+    }
+}
+