Bump copyright year to 2021

- Substitute occurrences of "-2020" with "-2021" using:
  git grep -I -l -e '-2020' -- ':(exclude)*.bak' | xargs \
  sed -b -i -e 's/-2020/-2021/g'

CUETools.Codecs.ALAC/ALACDotNet.cs

@@ -7,7 +7,7 @@ using CUETools.Codecs;
 using System.ComponentModel;
 using Newtonsoft.Json;
 
-//Copyright (c) 2008-2020 Grigory Chudov.
+//Copyright (c) 2008-2021 Grigory Chudov.
 //This library is based on ALAC decoder by David Hammerton.
 //See http://crazney.net/programs/itunes/alac.html for details.
 //Copyright (c) 2004 David Hammerton.

CUETools.Codecs.ALAC/ALACWriter.cs

@@ -1,6 +1,6 @@
 /**
  * CUETools.Codecs.ALAC: pure managed ALAC audio encoder
- * Copyright (c) 2009-2020 Grigory Chudov
+ * Copyright (c) 2009-2021 Grigory Chudov
  * Based on ffdshow ALAC audio encoder
  * Copyright (c) 2008  Jaikrishnan Menon, realityman@gmx.net
  *

CUETools.Codecs.ALAC/Alac.cs

@@ -1,6 +1,6 @@
 /**
  * CUETools.Codecs.ALAC: pure managed ALAC audio encoder
- * Copyright (c) 2009-2020 Grigory Chudov
+ * Copyright (c) 2009-2021 Grigory Chudov
  * Based on ffdshow ALAC audio encoder
  * Copyright (c) 2008  Jaikrishnan Menon, realityman@gmx.net
  *

CUETools.Codecs.ALAC/CUETools.Codecs.ALAC.csproj

@@ -7,7 +7,7 @@
     <RootNamespace>CUETools.Codecs</RootNamespace>
     <Product>CUETools</Product>
     <Description>A library for encoding and decoding ALAC.</Description>
-    <Copyright>Copyright (c) 2008-2020 Grigory Chudov</Copyright>
+    <Copyright>Copyright (c) 2008-2021 Grigory Chudov</Copyright>
     <Authors>Grigory Chudov</Authors>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <OutputPath>..\bin\$(Configuration)\plugins</OutputPath>