presentation: fix use-template example

Fixes unidoc#159

presentation/open.go

@@ -20,7 +20,7 @@ func OpenTemplate(fn string) (*Presentation, error) {
 	return p, nil
 }
 
-// Open opens and reads a document from a file (.docx).
+// Open opens and reads a document from a file (.pptx).
 func Open(filename string) (*Presentation, error) {
 	f, err := os.Open(filename)
 	if err != nil {

presentation/presentation.go

@@ -45,26 +45,28 @@ type Presentation struct {
 	themeRels  []common.Relationships
 }
 
-// New initializes and reurns a new presentation
-func New() *Presentation {
+func newEmpty() *Presentation {
 	p := &Presentation{x: pml.NewPresentation()}
-
 	p.x.SldIdLst = pml.NewCT_SlideIdList()
 	p.x.ConformanceAttr = sharedTypes.ST_ConformanceClassTransitional
 	p.AppProperties = common.NewAppProperties()
 	p.CoreProperties = common.NewCoreProperties()
 	p.ContentTypes = common.NewContentTypes()
+	p.Rels = common.NewRelationships()
+	p.prels = common.NewRelationships()
+	return p
+}
 
-	p.ContentTypes.AddOverride("/ppt/presentation.xml", "application/vnd.openxmlformats-officedocument.presentationml.presentation.main+xml")
+// New initializes and reurns a new presentation
+func New() *Presentation {
+	p := newEmpty()
 
-	p.Rels = common.NewRelationships()
+	p.ContentTypes.AddOverride("/ppt/presentation.xml", "application/vnd.openxmlformats-officedocument.presentationml.presentation.main+xml")
 
 	p.Rels.AddRelationship("docProps/core.xml", "http://schemas.openxmlformats.org/package/2006/relationships/metadata/core-properties")
 	p.Rels.AddRelationship("docProps/app.xml", "http://schemas.openxmlformats.org/officeDocument/2006/relationships/extended-properties")
 	p.Rels.AddRelationship("ppt/presentation.xml", "http://schemas.openxmlformats.org/officeDocument/2006/relationships/officeDocument")
 
-	p.prels = common.NewRelationships()
-
 	p.x.SldMasterIdLst = pml.NewCT_SlideMasterIdList()
 	m := pml.NewSldMaster()
 	m.ClrMap.Bg1Attr = dml.ST_ColorSchemeIndexLt1

presentation/read.go

@@ -19,7 +19,7 @@ import (
 
 // Read reads a document from an io.Reader.
 func Read(r io.ReaderAt, size int64) (*Presentation, error) {
-	doc := New()
+	doc := newEmpty()
 
 	td, err := ioutil.TempDir("", "gooxml-pptx")
 	if err != nil {