Update seekable API to simplify IO

lib/common/error_private.c

@@ -39,7 +39,7 @@ const char* ERR_getErrorString(ERR_enum code)
     case PREFIX(dictionary_wrong): return "Dictionary mismatch";
     case PREFIX(dictionaryCreation_failed): return "Cannot create Dictionary from provided samples";
     case PREFIX(frameIndex_tooLarge): return "Frame index is too large";
-    case PREFIX(needSeek): return "Wrong file position, a seek is required to continue";
+    case PREFIX(seekableIO): return "An I/O error occurred when reading/seeking";
     case PREFIX(maxCode):
     default: return notErrorCode;
     }

lib/common/zstd_errors.h

@@ -59,7 +59,7 @@ typedef enum {
   ZSTD_error_dictionary_wrong,
   ZSTD_error_dictionaryCreation_failed,
   ZSTD_error_frameIndex_tooLarge,
-  ZSTD_error_needSeek,
+  ZSTD_error_seekableIO,
   ZSTD_error_maxCode
 } ZSTD_ErrorCode;