Update copyright information for Zcash, leveldb, and libsnark.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

contrib/debian/copyright

@@ -8,18 +8,15 @@ Copyright: 2016-2019, The Zcash developers
  2009-2019, Bitcoin Core developers
  2009-2019, Bitcoin Developers
 License: Expat
-Comment: The Bitcoin Core developers encompasses the current developers listed on bitcoin.org,
- as well as the numerous contributors to the project.
- The Zcash developers are listed at https://z.cash/team.html.
+Comment: The Bitcoin Core developers encompasses the current developers listed on
+ bitcoin.org, as well as the numerous contributors to the project.
+ The Zcash developers are listed at https://z.cash/team.html and in doc/authors.md.
+ This copyright entry excludes files explicitly listed below.
 
 Files: depends/sources/libsodium-*.tar.gz
 Copyright: 2013-2016 Frank Denis
 License: ISC
 
-Files: depends/sources/libsnark-*.tar.gz
-Copyright: 2012-2016 SCIPR Lab and contributors; 2016 The Zcash developers
-License: Expat
-
 Files: depends/sources/gmp-*.tar.bz2
 Copyright: 1991, 1996, 1999, 2000, 2007 Free Software Foundation, Inc.
 License: LGPL
@@ -68,6 +65,16 @@ Files: src/secp256k1/build-aux/m4/ax_prog_cc_for_build.m4
 Copyright: 2008 Paolo Bonzini <bonzini@gnu.org>
 License: GNU-All-permissive-License
 
+Files src/leveldb/*
+Copyright: 2011, The LevelDB Authors
+License: BSD-3clause-Google
+Comment: The LevelDB Authors are listed in src/leveldb/AUTHORS.
+
+Files src/snark/*
+Copyright: 2012-2019, SCIPR Lab and contributors
+License: Expat
+Comment: The contributors are listed in src/snark/AUTHORS.
+
 License: Boost-Software-License-1.0
  Permission is hereby granted, free of charge, to any person or organization
  obtaining a copy of the software and accompanying documentation covered by

src/snark/LICENSE

@@ -1,7 +1,7 @@
 The libsnark library is developed by SCIPR Lab (http://scipr-lab.org)
 and contributors.
 
-Copyright (c) 2012-2014 SCIPR Lab and contributors (see AUTHORS file).
+Copyright (c) 2012-2019 SCIPR Lab and contributors (see AUTHORS file).
 
 All files, with the exceptions below, are released under the MIT License: