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/telegram/updates/gap_buffer_test.go

@@ -0,0 +1,24 @@
+package updates
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGapBuffer(t *testing.T) {
+	buf := new(gapBuffer)
+	buf.Enable(1, 7)
+
+	require.True(t, buf.Consume(update{State: 4, Count: 3}))
+	require.Equal(t, []gap{{4, 7}}, buf.gaps)
+
+	require.False(t, buf.Consume(update{State: 1, Count: 1}))
+	require.Equal(t, []gap{{4, 7}}, buf.gaps)
+
+	require.False(t, buf.Consume(update{State: 8, Count: 1}))
+	require.Equal(t, []gap{{4, 7}}, buf.gaps)
+
+	require.True(t, buf.Consume(update{State: 7, Count: 3}))
+	require.Empty(t, buf.gaps)
+}