move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/constant/uploads.go

@@ -0,0 +1,22 @@
+package constant
+
+// https://core.telegram.org/api/files#uploading-files
+const (
+	// UploadMaxSmallSize is maximum size of small file.
+	//
+	// Use upload.saveBigFilePart in case the full size of the file is more than 10 MB
+	// and upload.saveFilePart for smaller files
+	UploadMaxSmallSize = 10 * 1024 * 1024 // 10 MB
+	// UploadMaxParts is maximum parts count.
+	//
+	// Each part should have a sequence number, file_part, with a value ranging from 0 to 3,999.
+	UploadMaxParts = 3999
+	// UploadPadding is part size padding.
+	//
+	// `part_size % 1024 = 0` (divisible by 1KB)
+	UploadPadding = 1024
+	// UploadMaxPartSize is maximum size of single part.
+	//
+	// `524288 % part_size = 0` (512KB must be evenly divisible by part_size)
+	UploadMaxPartSize = 524288
+)