Rename README, LICENSE, BUILDING text files

The IJG README file has been renamed to README.ijg, in order to avoid
confusion (many people were assuming that that was our project's README
file and weren't reading README-turbo.txt) and to lay the groundwork for
markdown versions of the libjpeg-turbo README and build instructions.
diff --git a/jfdctfst.c b/jfdctfst.c
index 4936d47..497f120 100644
--- a/jfdctfst.c
+++ b/jfdctfst.c
@@ -3,7 +3,8 @@
  *
  * Copyright (C) 1994-1996, Thomas G. Lane.
  * This file is part of the Independent JPEG Group's software.
- * For conditions of distribution and use, see the accompanying README file.
+ * For conditions of distribution and use, see the accompanying README.ijg
+ * file.
  *
  * This file contains a fast, not so accurate integer implementation of the
  * forward DCT (Discrete Cosine Transform).
@@ -15,8 +16,8 @@
  * This implementation is based on Arai, Agui, and Nakajima's algorithm for
  * scaled DCT.  Their original paper (Trans. IEICE E-71(11):1095) is in
  * Japanese, but the algorithm is described in the Pennebaker & Mitchell
- * JPEG textbook (see REFERENCES section in file README).  The following code
- * is based directly on figure 4-8 in P&M.
+ * JPEG textbook (see REFERENCES section in file README.ijg).  The following
+ * code is based directly on figure 4-8 in P&M.
  * While an 8-point DCT cannot be done in less than 11 multiplies, it is
  * possible to arrange the computation so that many of the multiplies are
  * simple scalings of the final outputs.  These multiplies can then be