Make project structure more Bazel-friendly

Move tests close to sources, rename source
directory from `src` to `graph_autodiff`.
This way the main Bazel library target is
`@cpp-graph-autodiff//graph_autodiff`.

src/BUILD.bazel → graph_autodiff/BUILD.bazel

@@ -25,3 +25,14 @@ proto_library(
     name = "graph_proto",
     srcs = ["graph.proto"],
 )
+
+cc_test(
+  name = "graph_autodiff_test",
+  size = "small",
+  srcs = ["graph_test.cpp"],
+  deps = [
+    "@abseil-cpp//absl/status:statusor",
+    "@googletest//:gtest_main",
+    "//graph_autodiff"
+  ],
+)

src/graph.cpp → graph_autodiff/graph.cpp

@@ -14,7 +14,7 @@ under certain conditions: see LICENSE.
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
 #include "fmt/core.h"
-#include "src/graph.pb.h"
+#include "graph_autodiff/graph.pb.h"
 
 using namespace graph_autodiff;
 namespace gpb = graph_proto;

src/graph.h → graph_autodiff/graph.h

@@ -16,7 +16,7 @@ under certain conditions: see LICENSE.
 #include "absl/container/flat_hash_map.h"
 #include "absl/status/status.h"
 #include "absl/status/statusor.h"
-#include "src/graph.pb.h"
+#include "graph_autodiff/graph.pb.h"
 
 /* A note on the use of shared_ptr<const T>
 

tests/test.cpp → graph_autodiff/graph_test.cpp

@@ -1,7 +1,7 @@
 #include <gtest/gtest.h>
 
 #include "absl/status/statusor.h"
-#include "src/graph.h"
+#include "graph_autodiff/graph.h"
 
 using namespace graph_autodiff;