Convert remaining comments in /src to doxygen format

- Update comments in checkpoints to be doxygen compatible
- Update comments in checkqueue to be doxygen compatible
- Update coins to be doxygen compatible
- Fix comment typo in crypter.h
- Update licenses/copyright dates

Closes #5325 #5184 #5183 #5182

src/base58.cpp

@@ -1,5 +1,5 @@
 // Copyright (c) 2014 The Bitcoin developers
-// Distributed under the MIT/X11 software license, see the accompanying
+// Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "base58.h"
@@ -15,7 +15,7 @@
 #include <boost/variant/apply_visitor.hpp>
 #include <boost/variant/static_visitor.hpp>
 
-/* All alphanumeric characters except for "0", "I", "O", and "l" */
+/** All alphanumeric characters except for "0", "I", "O", and "l" */
 static const char* pszBase58 = "123456789ABCDEFGHJKLMNPQRSTUVWXYZabcdefghijkmnopqrstuvwxyz";
 
 bool DecodeBase58(const char* psz, std::vector<unsigned char>& vch)