Prepare for Goldmark

This commmit prepares for the addition of Goldmark as the new Markdown renderer in Hugo.

This introduces a new `markup` package with some common interfaces and each implementation in its own package.

See #5963

markup/markup_test.go

@@ -0,0 +1,41 @@
+// Copyright 2019 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package markup
+
+import (
+	"testing"
+
+	"github.com/spf13/viper"
+
+	"github.com/gohugoio/hugo/markup/converter"
+
+	qt "github.com/frankban/quicktest"
+)
+
+func TestConverterRegistry(t *testing.T) {
+	c := qt.New(t)
+
+	r, err := NewConverterProvider(converter.ProviderConfig{Cfg: viper.New()})
+
+	c.Assert(err, qt.IsNil)
+
+	c.Assert(r.Get("foo"), qt.IsNil)
+	c.Assert(r.Get("markdown"), qt.Not(qt.IsNil))
+	c.Assert(r.Get("mmark"), qt.Not(qt.IsNil))
+	c.Assert(r.Get("asciidoc"), qt.Not(qt.IsNil))
+	c.Assert(r.Get("rst"), qt.Not(qt.IsNil))
+	c.Assert(r.Get("pandoc"), qt.Not(qt.IsNil))
+	c.Assert(r.Get("org"), qt.Not(qt.IsNil))
+
+}