argon2: use as submodule

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "argon2"]
+	path = argon2
+	url = https://github.com/P-H-C/phc-winner-argon2
+	ignore = dirty

CMakeLists.txt

@@ -74,17 +74,6 @@ list (APPEND opendht_SOURCES
     src/log.cpp
 )
 
-if (OPENDHT_ARGON2)
-    list (APPEND opendht_SOURCES
-        argon2/argon2.c
-        argon2/core.c
-        argon2/blake2/blake2b.c
-        argon2/thread.c
-        argon2/encoding.c
-        argon2/ref.c
-    )
-endif ()
-
 list (APPEND opendht_HEADERS
     include/opendht/def.h
     include/opendht/utils.h
@@ -116,12 +105,28 @@ configure_file (
     @ONLY
 )
 
-include_directories (
+include_directories(
     ./
     include/
     include/opendht/
     ${CMAKE_CURRENT_BINARY_DIR}/include/
 )
+if(OPENDHT_ARGON2)
+    # make sure argon2 submodule is up to date and initialized
+    message("Initializing Argon2 submodule")
+    execute_process(COMMAND git submodule update --init)
+
+    # add local argon2 files to build
+    list (APPEND opendht_SOURCES
+        argon2/src/argon2.c
+        argon2/src/core.c
+        argon2/src/blake2/blake2b.c
+        argon2/src/thread.c
+        argon2/src/ref.c
+        argon2/src/encoding.c
+    )
+    include_directories(argon2/include/)
+endif()
 
 if (NOT DEFINED CMAKE_INSTALL_LIBDIR)
     set(CMAKE_INSTALL_LIBDIR lib)

Makefile.am

@@ -2,10 +2,6 @@ AM_CXXFLAGS = -pthread
 
 SUBDIRS =
 
-if WITH_INCLUDED_ARGON2
-SUBDIRS += argon2
-endif
-
 SUBDIRS += src
 
 if ENABLE_TOOLS