If not set `XDG_DATA_HOME` is defaulted to `~/.local/share`; the data are stored under the `$XDG_DATA_HOME/nvim`.

TODO: Only works at startup (i.e., in the user's init.vim/vimrc/--cmd),
      but it should probably work at any time.

---

patch 7.4.1799
Problem:    'guicolors' is a confusing option name.
Solution:   Use 'termguicolors' instead. (Hirohito Higashi)
https://github.com/vim/vim/commit/61be73bb0f965a895bfb064ea3e55476ac175162

patch 7.4.1806
Problem:    'termguicolors' option missing from the options window.
Solution:   Add the entry.
https://github.com/vim/vim/commit/8e3d1b6326c103cc92f8d07b1161ee5172acf201

patch 7.4.1808
Problem:    Using wrong feature name to check for 'termguicolors'.
Solution:   Use the right feature name. (Ken Takata)
https://github.com/vim/vim/commit/8a24b794b89916c8074892e7b25121a21f1fa9c9

patch 7.4.1809
Problem:    Using wrong short option name for 'termguicolors'.
Solution:   Use the option name.
https://github.com/vim/vim/commit/868cfc19bb079a16ca58884b551486566f35419b

Wrapping it will send it to the terminal "directly", which might change the
cursor of another pane, e.g. when starting Neovim and changing to
another pane directly.

tmux has a terminfo extension (Ss/Se) to handle and translate the
DECSCUSR sequences internally.  This can be controlled through
`terminal-overrides`, but does not appear to be able to handle the
uncommon sequences for Konsole.

Although UNIX is a registered trademark of The Open Group, it doesn't
really matter whether we refer to these systems as UNIX, Unix, or
Unix-like. So, for consistency, refer to them collectively as Unix.

Related:
http://www.greens.org/about/unix.html
http://www.unixica.com/html/unixunix.html

"vimrc" refers to all files that are used to configure Neovim. The main
configuration file is init.vim nowadays.

All nvimrc references that are left refer to a local ".nvimrc" which is read
if 'exrc' is set. ".ngvimrc" references were completely wiped.

Closes #3552.

Helped-by: Justin M. Keyes <justinkz@gmail.com>
Helped-by: ZyX <kp-pav@yandex.ru>

Besides some minor rewording, this commit does the following:

- the argument to the `q' flag is optional, so denote it as such
- the cross references to vim (`.Xr vim 1') were pointless, just refer
  to it as `Vim'
- the `d' flag doesn't actually take any arguments; `nvim -d' works
  just fine, so make the manual reflect that
- the `L' flag is just an alias for the `r' flag, so clarify that
- there was a lot of redundancy between the `o', `O', and `p' flags,
  unify their descriptions a bit

Helped-by: Justin M. Keyes <justinkz@gmail.com>

[ci skip]

igor(1) checks if the document date is today, so this should prevent
forgetting to bump the date in the future.