This allows users to define behaviors for arbitrary registers. These
registers can be any character including multibyte characters. This
means that any character may be used as a register and if that register
is not a builtin register, it will defer to a user-defined vimscript
function for behavior.

This is done throw an option called 'userregfun'

The function that 'userregfun' defines is a function that takes 3
arguments:

   action - Either set to "put" or "yank"
   register - The character representing the register.
   content - If the action is "yank" this string contains the content
             yanked.

Multibyte registers are still broken for expressions. So while

  let @&=xyz

Works as expected,

  let @λ=xyz

will still throw a parse error.

This option allows a character to be displayed in the colorcolumn. This
allows the colorcolumn ot have a traditional line if the colorcolumn
character is set to a vertical line '│' or even a series of dots for a
':'.

The option is a part of the 'listchars' setting under the name
'colorcol'. So 'set listchars=colorcol:│' will work.

* fix function parameter comments
* remove space after star in function names

Problem:    Cannot get composing characters from the screen.
Solution:   Add screenchars() and screenstring(). (partly by Ozaki Kiichi,
            closes vim/vim#4059)
https://github.com/vim/vim/commit/2912abb3a2fd72074e3901c8ae1d4a77ce764675

Problem:    User function completion fails with dict function.
Solution:   Do not stop sequencing through the list if user functions when
            encountering an empty name. (Naohiro Ono, closes vim/vim#8765,
            closes vim/vim#8774)
https://github.com/vim/vim/commit/5aec755b678cfd434b8ea2158d06992f33e1ff80

Problem:    Completing "call g:" returns entries with just "g:". (Naohiro Ono)
Solution:   Skip empty strings returned by get_user_func_name(). (closes vim/vim#8753)
https://github.com/vim/vim/commit/069f90852f1444cac50491c10dfbd339a3f9e0c8

Port VimL's Blob type - vim-patch:8.1.{0735,0736,0738,0741,0742,0755,0756,0757,0765,0793,0797,0798,0802,1022,1023,1671},8.2.{0121,0184,0404,0521,0829,1473,1866,2712}

Problem:    Vim9: appending to pushed blob gives wrong result.
Solution:   Set ga_maxlen when copying a blob.
https://github.com/vim/vim/commit/66fa5fd54f550c0790d36c20124c49493b323bfa

Vim9script is N/A.