Fix methods being mistakenly called routines

Resolves #484.

@subkinds is an array like:

    [Array[Str].new("method"), Array[Str].new("method")]

The code checks if there's more than one element and falls back to
relatively safe “routine” word. However, in this case there are
multiple items and all of them are methods, so let's squish the whole
thing before performing the check (using yet undocumented “with”
parameter, see #1490).

There were many methods affected by this.

htmlify.p6

@@ -918,7 +918,9 @@ sub write-kind($kind) {
         .categorize({.name})
         .kv.map: -> $name, @docs {
             my @subkinds = @docs.map({.subkinds}).unique;
-            my $subkind = @subkinds.elems == 1 ?? @subkinds.list[0] !! $kind;
+            my $subkind = @subkinds.squish(with => &infix:<~~>) == 1
+                          ?? @subkinds.list[0]
+                          !! $kind;
             my $pod = pod-with-title(
                 "Documentation for $subkind $name",
                 pod-block("Documentation for $subkind $name, assembled from the following types:"),