Self-spec refactoring

Reflect piqi.org -> piqi directory renaming in README

README

@@ -101,7 +101,7 @@ FILES
   piqicc/               Piqi compiler compiler
   piqic/                Piq interface compiler for OCaml and Erlang
   piqi-tools/           "piqi" command-line utility (piqi tools)
-  piqi.org/             Piqi self-specification
+  piqi                  Piqi self-specification
   piqilib/              Piqi common library
   piqirun-ocaml/        Piqi runtime library for OCaml
   piqi-erlang/          Piqi runtime library and Piqi tools bindings for Erlang