moved IO related code to stand-alone file, piped all read/and writes

through new API, /rad_log now can enable read and/or write logs with
"io", "io_reads", "io_writes" parameters.

src/linker/lnk_log.h

@@ -9,7 +9,8 @@ typedef enum
   LNK_Log_Debug,
   LNK_Log_InputObj,
   LNK_Log_InputLib,
-  LNK_Log_IO,
+  LNK_Log_IO_Read,
+  LNK_Log_IO_Write,
   LNK_Log_SizeBreakdown,
   LNK_Log_LinkStats,
   LNK_Log_Timers,