Rename COPYING.txt to LICENSE for opensource compliance and update links

in README.txt.

Makefile.am

@@ -40,7 +40,7 @@ EXTRA_DIST =                                                                 \
   generate_descriptor_proto.sh                                               \
   README.txt                                                                 \
   INSTALL.txt                                                                \
-  COPYING.txt                                                                \
+  LICENSE                                                                    \
   CONTRIBUTORS.txt                                                           \
   CHANGES.txt                                                                \
   editors/README.txt                                                         \

README.txt

@@ -1,6 +1,6 @@
 Protocol Buffers - Google's data interchange format
 Copyright 2008 Google Inc.
-http://code.google.com/apis/protocolbuffers/
+https://developers.google.com/protocol-buffers/
 
 C++ Installation - Unix
 =======================
@@ -149,4 +149,4 @@ Usage
 The complete documentation for Protocol Buffers is available via the
 web at:
 
-  http://code.google.com/apis/protocolbuffers/
+  https://developers.google.com/protocol-buffers/