net: implement the necessary parts of the I2P SAM protocol

Implement the following commands from the I2P SAM protocol:

* HELLO: needed for all of the remaining ones
* DEST GENERATE: to generate our private key and destination
* NAMING LOOKUP: to convert .i2p addresses to destinations
* SESSION CREATE: needed for STREAM CONNECT and STREAM ACCEPT
* STREAM CONNECT: to make outgoing connections
* STREAM ACCEPT: to accept incoming connections

src/logging.cpp

@@ -156,6 +156,7 @@ const CLogCategoryDesc LogCategories[] =
     {BCLog::QT, "qt"},
     {BCLog::LEVELDB, "leveldb"},
     {BCLog::VALIDATION, "validation"},
+    {BCLog::I2P, "i2p"},
     {BCLog::ALL, "1"},
     {BCLog::ALL, "all"},
 };