Problem:    String interpolation in :def function may fail.
Solution:   Do not terminate the expression. (closes #10377)

Problem:    Popup_hide() does not always have effect.
Solution:   Add the POPF_HIDDEN_FORCE flag. (closes #10376)

Problem:    Using execute() to define a lambda doesn't work. (Ernie Rael)
Solution:   Put the getline function in evalarg. (closes #10375)

Problem:    The mode #defines are not clearly named.
Solution:   Prepend MODE_.  Renumber them to put the mapped modes first.

Problem:    Imperfect coding.
Solution:   Make code nicer.

Problem:    MODE_ enum entries names are too generic.
Solution:   use CH_MODE_.

Problem:    No text formatting for // comment after a statement.
Solution:   format a comment when the 'c' flag is in 'formatoptions'.

Problem:    Some users do not want a line comment always inserted.
Solution:   Add the '/' flag to 'formatoptions' to not repeat the comment
            leader after a statement when using "o".

Problem:    MS-Windows: cannot use transparent background.
Solution:   Make transparent background work with 'termguicolors' and NONE
            background color. (Yasuhiro Matsumoto, closes #10310, closes #7162)