Proposal: log binary data for Solidity

The program_id is not needed on "Program return data: " because it
always preceeded by the program invoke message, so no need to repeat
the program id. Also rename this to "Program return: " since "data"
is redundant.

sdk/bpf/c/inc/sol/log.h

@@ -40,6 +40,11 @@ static void sol_log_array(const uint8_t *array, int len) {
   }
 }
 
+/**
+ * Print the base64 representation of some arrays.
+ */
+void sol_log_data(SolBytes *fields, uint64_t fields_len);
+
 /**
  * Prints the program's input parameters
  *