Add DecodeMeta function for decoding metadata from an io.Reader.

meta.go

@@ -1,5 +1,6 @@
 package step
 
+import "io"
 import "strconv"
 import "strings"
 
@@ -70,3 +71,10 @@ func ParseMeta (input string) (Meta, error) {
 	}
 	return meta, nil
 }
+
+// DecodeMeta decodes metadata from an io.Reader. The entire reader is consumed.
+func DecodeMeta (input io.Reader) (Meta, error) {
+	buffer, err := io.ReadAll(input)
+	if err != nil { return nil, err }
+	return ParseMeta(string(buffer))
+}