build: Refactor the build structure of the project

Moved all header files to `include` and all cpp files to `src`.
Updated the meson.build accordingly.

Change-Id: I9e26197b9c73b5e284cfc9d0d78a234546c282ad
Signed-off-by: Willy Tu <wltu@google.com>
diff --git a/proto/meson.build b/proto/meson.build
index 0600083..02d46d9 100644
--- a/proto/meson.build
+++ b/proto/meson.build
@@ -1,4 +1,4 @@
-proto = custom_target(
+src_pb = custom_target(
   'proto',
   command: [
     find_program('protoc', native: true),
@@ -11,3 +11,20 @@
     'binaryblob.pb.h',
   ],
   input: 'binaryblob.proto')
+
+binaryblobproto_pre = declare_dependency(
+  include_directories: include_directories('.'),
+  dependencies: dependency('protobuf')
+)
+
+binaryblobproto_lib = static_library(
+  'binaryblob_proto',
+  src_pb,
+  implicit_include_directories: false,
+  dependencies: binaryblobproto_pre
+)
+
+binaryblobproto_dep = declare_dependency(
+  dependencies: binaryblobproto_pre,
+  link_with: binaryblobproto_lib
+)