add todos in third_party

Author: michlee1337

third_party/base64/base64.h

@@ -2,6 +2,7 @@
 //  base64 encoding and decoding with C++.
 //  Version: 2.rc.04 (release candidate)
 //
+// TODO (#51): Switch to MIT base64 lib for faster performance
 
 #ifndef BASE64_H_C0CE2A47_D10E_42C9_A27C_C883944E704A
 #define BASE64_H_C0CE2A47_D10E_42C9_A27C_C883944E704A

third_party/statusor/statusor.h

@@ -78,6 +78,7 @@
 #include "absl/base/attributes.h"
 #include "absl/base/macros.h"
 
+// TODO (#61): Switch to official absl::StatusOr release when available
 namespace cloudevents_absl {
 
 // Returned StatusOr objects may not be ignored.