Move the licenses around a bit, potentially structuring for Valve

to drop in a top level license file.

LICENSE

@@ -0,0 +1,12 @@
+Copyright (c) 2018, Valve Corporation
+All rights reserved.
+
+Redistribution and use of Proton in source and binary forms is governed
+by a variety of licenses.
+
+Refer to the contents of LICENCE.proton for the license for the top
+level contents of the Proton project.
+
+Proton uses a variety of other software, each of which is governed
+by its own license.  Those licenses are contained in a file named
+LICENSE at the top of each directory.

LICENSE.proton

@@ -0,0 +1 @@
+TODO - Valve to provide a license for Proton itself.  Similar to openvr license?

build_proton.sh

@@ -491,9 +491,9 @@ if [ "$PACKAGE" = true ]; then
     cp -a filelock.py dist/
     cp -a proton dist/
     if [ "$PLATFORM" == "Darwin" ]; then
-    cp -a LICENSE.osx dist/LICENSE
+    cp -a dist.LICENSE.osx dist/LICENSE
     else
-    cp -a LICENSE.lin dist/LICENSE
+    cp -a dist.LICENSE.lin dist/LICENSE
     fi
     date '+%s' > dist/version