Implemented "php" tags for structs (#20)
If you marshal or unmarshal from/into a struct, you may want to use go tags for it, instead of staticly using the struct field names just changing the first letter to upper/lower case.
Example:
type Target struct {
FirstName string `php:"vorname"`
LastName string `php:"nachname"`
}
This will correctly be filled with the according fields of serialized php object.
Also unmarshaling will not fail if a struct field does not exist, because you may want to skip some fields from php objects.
