hugolib: Implement "related content"

This closes #98, even if this commit does not do full content text search.

We may revisit that problem in the future, but that deserves its own issue.

Fixes #98

tpl/collections/collections.go

@@ -23,6 +23,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/gohugoio/hugo/common/types"
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/helpers"
 	"github.com/spf13/cast"
@@ -641,3 +642,8 @@ func (ns *Namespace) Uniq(l interface{}) (interface{}, error) {
 	}
 	return ret.Interface(), nil
 }
+
+// KeyVals creates a key and values wrapper.
+func (ns *Namespace) KeyVals(key interface{}, vals ...interface{}) (types.KeyValues, error) {
+	return types.KeyValues{Key: key, Values: vals}, nil
+}

tpl/collections/init.go

@@ -63,6 +63,13 @@ func init() {
 			[][2]string{},
 		)
 
+		ns.AddMethodMapping(ctx.KeyVals,
+			[]string{"keyVals"},
+			[][2]string{
+				{`{{ keyVals "key" "a" "b" }}`, `key: [a b]`},
+			},
+		)
+
 		ns.AddMethodMapping(ctx.In,
 			[]string{"in"},
 			[][2]string{