Misc config loading fixes

The main motivation behind this is simplicity and correctnes, but the new small config library is also faster:

```
BenchmarkDefaultConfigProvider/Viper-16         	  252418	      4546 ns/op	    2720 B/op	      30 allocs/op
BenchmarkDefaultConfigProvider/Custom-16        	  450756	      2651 ns/op	    1008 B/op	       6 allocs/op
```

Fixes #8633
Fixes #8618
Fixes #8630
Updates #8591
Closes #6680
Closes #5192

commands/commandeer.go

@@ -410,7 +410,5 @@ func (c *commandeer) loadConfig(mustHaveConfigFile, running bool) error {
 	}
 	config.Set("cacheDir", cacheDir)
 
-	cfg.Logger.Infoln("Using config file:", config.ConfigFileUsed())
-
 	return nil
 }

commands/commands_test.go

@@ -20,6 +20,8 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/gohugoio/hugo/config"
+
 	"github.com/gohugoio/hugo/htesting"
 
 	"github.com/spf13/afero"
@@ -29,7 +31,6 @@ import (
 	"github.com/gohugoio/hugo/common/types"
 
 	"github.com/spf13/cobra"
-	"github.com/spf13/viper"
 
 	qt "github.com/frankban/quicktest"
 )
@@ -166,7 +167,7 @@ func TestFlags(t *testing.T) {
 			name: "ignoreVendor as bool",
 			args: []string{"server", "--ignoreVendor"},
 			check: func(c *qt.C, cmd *serverCmd) {
-				cfg := viper.New()
+				cfg := config.New()
 				cmd.flagsToConfig(cfg)
 				c.Assert(cfg.Get("ignoreVendor"), qt.Equals, true)
 			},
@@ -176,7 +177,7 @@ func TestFlags(t *testing.T) {
 			name: "ignoreVendorPaths",
 			args: []string{"server", "--ignoreVendorPaths=github.com/**"},
 			check: func(c *qt.C, cmd *serverCmd) {
-				cfg := viper.New()
+				cfg := config.New()
 				cmd.flagsToConfig(cfg)
 				c.Assert(cfg.Get("ignoreVendorPaths"), qt.Equals, "github.com/**")
 			},
@@ -216,7 +217,7 @@ func TestFlags(t *testing.T) {
 				c.Assert(sc.serverPort, qt.Equals, 1366)
 				c.Assert(sc.environment, qt.Equals, "testing")
 
-				cfg := viper.New()
+				cfg := config.New()
 				sc.flagsToConfig(cfg)
 				c.Assert(cfg.GetString("publishDir"), qt.Equals, "/tmp/mydestination")
 				c.Assert(cfg.GetString("contentDir"), qt.Equals, "mycontent")

commands/config.go

@@ -22,13 +22,14 @@ import (
 	"sort"
 	"strings"
 
+	"github.com/gohugoio/hugo/common/maps"
+
 	"github.com/gohugoio/hugo/parser"
 	"github.com/gohugoio/hugo/parser/metadecoders"
 
 	"github.com/gohugoio/hugo/modules"
 
 	"github.com/spf13/cobra"
-	"github.com/spf13/viper"
 )
 
 var _ cmder = (*configCmd)(nil)
@@ -81,7 +82,7 @@ func (c *configCmd) printConfig(cmd *cobra.Command, args []string) error {
 		return err
 	}
 
-	allSettings := cfg.Cfg.(*viper.Viper).AllSettings()
+	allSettings := cfg.Cfg.Get("").(maps.Params)
 
 	// We need to clean up this, but we store objects in the config that
 	// isn't really interesting to the end user, so filter these.

commands/new_site.go

@@ -19,6 +19,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/parser/metadecoders"
 
 	_errors "github.com/pkg/errors"
@@ -29,7 +30,6 @@ import (
 	"github.com/gohugoio/hugo/parser"
 	"github.com/spf13/cobra"
 	jww "github.com/spf13/jwalterweatherman"
-	"github.com/spf13/viper"
 )
 
 var _ cmder = (*newSiteCmd)(nil)
@@ -123,7 +123,7 @@ func (n *newSiteCmd) newSite(cmd *cobra.Command, args []string) error {
 
 	forceNew, _ := cmd.Flags().GetBool("force")
 
-	return n.doNewSite(hugofs.NewDefault(viper.New()), createpath, forceNew)
+	return n.doNewSite(hugofs.NewDefault(config.New()), createpath, forceNew)
 }
 
 func createConfig(fs *hugofs.Fs, inpath string, kind string) (err error) {

commands/server_test.go

@@ -22,10 +22,10 @@ import (
 	"testing"
 	"time"
 
+	"github.com/gohugoio/hugo/config"
 	"github.com/gohugoio/hugo/helpers"
 
 	qt "github.com/frankban/quicktest"
-	"github.com/spf13/viper"
 )
 
 func TestServer(t *testing.T) {
@@ -101,7 +101,7 @@ func TestFixURL(t *testing.T) {
 		t.Run(test.TestName, func(t *testing.T) {
 			b := newCommandsBuilder()
 			s := b.newServerCmd()
-			v := viper.New()
+			v := config.New()
 			baseURL := test.CLIBaseURL
 			v.Set("baseURL", test.CfgBaseURL)
 			s.serverAppend = test.AppendPort