This commit allows buffers that were not previously written to disk to
be restored if a backup has been generated in their name. Consequently,
we got rid of a few non-POSIX calls to `find` (using `-maxdepth` or
`-delete`), and of the logic that detected the newest backup (which
didn't seem a good reason enough to steer away from a portable command).
Fixes#1236
No defaults have been altered, just added the ability to do user override. The existing facespec had a background of 'black', which ends up looking a little harsh for people who do black text on a white background.
The option is now used as a fallback when detection by extension fails. Some
scripts like `base/mail.kak` and `base/html.kak` still rely heavily on it.
Builtin support for `flake8` can be obtained using the following:
```
set window lintcmd 'flake8 --filename=* --format="%(path)s:%(row)d:%(col)d: error: %(text)s"'
```
Initialising the `comment_line_chars` and `comment_selection_chars` variables
in language support scripts created a hard dependency of those scripts
to `commenting.kak`, which would create errors when this script was not
loaded, e.g. when running tests.
Level out the builtin commands loaded at startup in terms of format and
expressiveness. The following convention was followed:
* commands that take more than one argument have to be described along
with their parameters prior to the actual documentation, otherwise the
docstring consists in a capitalized sentence
e.g. `command <arg1>: do something`
* optional arguments are enclosed in square brackets, to comply with the
format used for hardcoded commands
e.g. `cd [<directory>]`
* describe the effects of the command in the documentation string and
omit implementation details unless they are relevant. Usually command
names include the name of the tool they use, so they don't need to be
redundantly mentioned
e.g. `tmux-new-pane <arguments>: open a new pane`
* document the format the parameters to the commands, or list them if
they are to be chosen among a list of static values (c.f. `spell.kak`)
