This commit properly produces backslash characters within double quote
strings instead of hoping the shell will not recognize the escape
sequence that they form with the following character. Use the proper
POSIX function declaration form.
The uncommenting logic now also ignores trailing newline characters,
which shortens the amount of operations needed to uncomment a selection.
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.
Initializing the `formatcmd` variable in the default language support
scripts created a dependency to the `formatter.kak` script, which we do
not want. Examples of such cases are when users haven't loaded the
`formatter.kak` script, or when Kakoune runs its test suite and
selectively loads some language scripts for testing purposes.
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`)
