Add support for FuncMap

Makefile

@@ -0,0 +1,10 @@
+all: fmt vet test
+
+fmt:
+	go fmt ./...
+
+vet:
+	go vet ./...
+
+test:
+	go test -vet=off ./...

loader.go

@@ -23,6 +23,7 @@ type Collection struct {
 type Options struct {
 	// Files from shared collections will be available in every main template.
 	SharedCollections []Collection
+	FuncMap           template.FuncMap
 }
 
 // Load templates from specified directories with default options.
@@ -38,6 +39,7 @@ func LoadWithOptions(
 	options Options,
 ) (map[string]*template.Template, error) {
 	sharedTemplate := template.New("")
+
 	for _, stp := range options.SharedCollections {
 		files, err := getFiles(stp.RootDir, stp.Prefix)
 		if err != nil {
@@ -45,7 +47,12 @@ func LoadWithOptions(
 		}
 
 		for name, contents := range files {
-			sharedTemplate, err = sharedTemplate.New(name).Parse(contents)
+			sharedTemplate = sharedTemplate.New(name)
+			if options.FuncMap != nil {
+				sharedTemplate = sharedTemplate.Funcs(options.FuncMap)
+			}
+
+			sharedTemplate, err = sharedTemplate.Parse(contents)
 			if err != nil {
 				return nil, err
 			}