Detect multiple subkinds on routines + note if a subkind can't be found

This is useful for those routines defined as both a sub and method, of
which Perl 6 has many

htmlify.p6

@@ -317,16 +317,18 @@ sub write-type-file(:$dr, :$what, :$pod, :$podname) {
             );
         } else {
             # determine whether it's a sub or method
-            my Str $subkind;
+            my Str @subkind;
             {
                 my %counter;
                 for first-code-block($chunk).lines {
                     if ms/^ 'multi'? (sub|method)»/ {
                         %counter{$0}++;
                     }
                 }
-                if %counter == 1 {
-                    ($subkind,) = %counter.keys;
+                if +%counter {
+                    @subkind = %counter.keys;
+                } else {
+                    note "The subkind of routine $name in $podname.pod cannot be determined."
                 }
                 if %counter<method> {
                     write-qualified-method-call(
@@ -339,7 +341,7 @@ sub write-type-file(:$dr, :$what, :$pod, :$podname) {
 
             $dr.add-new(
                 :kind<routine>,
-                :$subkind,
+                :@subkind,
                 :$name,
                 :pod($chunk),
                 :!pod-is-complete,

lib/Perl6/Documentable.pm

@@ -1,7 +1,7 @@
 use URI::Escape;
 class Perl6::Documentable {
     has Str $.kind;     # type, language doc, routine, operator
-    has Str $.subkind;  # class/role/enum, sub/method, prefix/infix/...
+    has Str @.subkind;  # class/role/enum, sub/method, prefix/infix/...
 
     has Str $.name;
     has Str $.url;
@@ -14,7 +14,7 @@ class Perl6::Documentable {
 
     method human-kind() {   # SCNR
         $.kind eq 'operator'
-            ?? "$.subkind operator"
+            ?? "@.subkind[] operator"
             !! $.kind eq 'language'
             ?? 'language documentation'
             !! $.subkind // $.kind;
@@ -28,7 +28,7 @@ class Perl6::Documentable {
     }
     method url() {
         $!url //= $.kind eq 'operator'
-            ?? "/language/operators#" ~ uri_escape("$.subkind $.name".subst(/\s+/, '_', :g))
+            ?? "/language/operators#" ~ uri_escape("@.subkind[] $.name".subst(/\s+/, '_', :g))
             !! "/$.kind/$.name"
             ;
     }