Implement TLS support using Botan

For now, it tries two TLS ports and then connects to the non-tls port.  In
the future we would like the user to be able to configure that.

fix #2435

CMakeLists.txt

@@ -21,6 +21,7 @@ find_package(Iconv REQUIRED)
 find_package(Libuuid REQUIRED)
 find_package(Libidn)
 find_package(SystemdDaemon)
+find_package(Botan)
 
 # To be able to include the config.h file generated by cmake
 include_directories("${CMAKE_CURRENT_SOURCE_DIR}/src/")
@@ -37,6 +38,10 @@ if(SYSTEMDDAEMON_FOUND)
   include_directories(${SYSTEMDDAEMON_INCLUDE_DIRS})
 endif()
 
+if(BOTAN_FOUND)
+  include_directories(${BOTAN_INCLUDE_DIRS})
+endif()
+
 set(POLLER_DOCSTRING "Choose the poller between POLL and EPOLL (Linux-only)")
 if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
  set(POLLER "EPOLL" CACHE STRING ${POLLER_DOCSTRING})
@@ -95,6 +100,9 @@ file(GLOB source_network
   src/network/*.[hc]pp)
 add_library(network STATIC ${source_network})
 target_link_libraries(network logger)
+if(BOTAN_FOUND)
+  target_link_libraries(network ${BOTAN_LIBRARIES})
+endif()
 
 #
 ## irclib