Allow go2idl to generate non-Go file types

Remove some indentation from file generation for specific languages,
allow SnippetWriter's io.Writer to be accessed, and add Path to
types.Name for languages where Package and Path can be disjoint.

cmd/libs/go2idl/generator/snippet_writer.go

@@ -116,6 +116,10 @@ func (s *SnippetWriter) Do(format string, args interface{}) *SnippetWriter {
 	return s
 }
 
+func (s *SnippetWriter) Out() io.Writer {
+	return s.w
+}
+
 // Error returns any encountered error.
 func (s *SnippetWriter) Error() error {
 	return s.err