Add flag to aos_dump and log_cat to print integers in hex format.

Define new --use_hex flag on aos_dump and log_cat applications that
controls how integers are formatted in the output.
Add use_hex field to JsonOptions struct used by FlatbufferToJson.
Update internal helpers used by FlatbufferToJson to act on new tag.

Change-Id: I26dea2cc37de3af4a1e10852e0df8ff93a696802
Signed-off-by: Austin Schuh <austin.schuh@bluerivertech.com>
diff --git a/aos/json_to_flatbuffer.h b/aos/json_to_flatbuffer.h
index 45920a8..d5e1039 100644
--- a/aos/json_to_flatbuffer.h
+++ b/aos/json_to_flatbuffer.h
@@ -45,6 +45,8 @@
   // more extensive version of multi_line that prints every single field on its
   // own line.
   bool max_multi_line = false;
+  // Will integers be printed in hexadecimal form instead of decimal.
+  bool use_hex = false;
 };
 
 // Converts a flatbuffer into a Json string.