patch 8.0.1850: todo items in source code not visible for users

Problem:    Todo items in source code not visible for users.
Solution:   Move the todo items to the help file.

runtime/doc/todo.txt

@@ -36,7 +36,26 @@ entered there will not be repeated below, unless there is extra information.
 -------------------- Known bugs and current work -----------------------
 
 Terminal emulator window:
-- Still some stuff to implement and bugs to fix, see src/terminal.c
+- Win32: Termdebug doesn't work, because gdb does not support mi2.  This
+  plugin: https://github.com/cpiger/NeoDebug  runs gdb as a job, redirecting
+  input and output.  Command I/O is in gdb window.
+- Win32: Redirecting input does not work, half of Test_terminal_redir_file()
+  is disabled.
+- Win32: Redirecting output works but includes escape sequences.
+- Win32: Make terminal used for :!cmd in the GUI work better.  Allow for
+  redirection.
+- Terminal API: Add more functionality? (Ozaki Kiichi 2018 May 13, #2907)
+- When the job only outputs lines, we could handle resizing the terminal
+  better: store lines separated by line breaks, instead of screen lines,
+  then when the window is resized redraw those lines.
+- Redrawing is slow with Athena and Motif. (Ramel Eshed)
+- For the GUI fill termios with default values, perhaps like pangoterm:
+  http://bazaar.launchpad.net/~leonerd/pangoterm/trunk/view/head:/main.c#L134
+- When 'encoding' is not utf-8, or the job is using another encoding, setup
+  conversions.
+- Termdebug does not work when Vim was build with mzscheme: gdb hangs just
+  after "run".  Everything else works, including communication channel.  Not
+  initializing mzscheme avoid the problem, thus it's not some #ifdef.
 
 Patch to refactor efm_to_regpat(). (Yegappan Lakshmanan, 2018 May 16, #2924)