Move more BN internals to bn_lcl.h

There was an unused macro in ssl_locl.h that used an internal
type, so I removed it.
Move bio_st from bio.h to ossl_type.h

Reviewed-by: Andy Polyakov <appro@openssl.org>
diff --git a/CHANGES b/CHANGES
index c400ba1..265fa8b 100644
--- a/CHANGES
+++ b/CHANGES
@@ -16,6 +16,9 @@
         RC2_SHORT, RC2_LONG, RC4_LONG, RC4_CHUNK, RC4_INDEX
      [Rich Salz, with advice from Andy Polyakov]
 
+  *) Many BN internals have been moved to an internal header file.
+     [Rich Salz with help from Andy Polyakov]
+
   *) Configuration and writing out the results from it has changed.
      Files such as Makefile include/openssl/opensslconf.h and are now
      produced through general templates, such as Makefile.in and