Add "iskeyword" option

[fukamachi]

Description

Add "iskeyword" of vi-mode option, which is used to specify a character set to be treated as a word by vi-mode.

• Type: a list of strings
• Default: @,48-57,_,192-255
• Alias: isk

Usage

It can be set in ex mode, like :set iskeyword=@,_. Be sure it must be a comma-separated string in ex mode.

In this PR, several set operations like +=, -=, ^= are also added, which can be used like :set iskeyword+=@-@ to add a new value.

To set in init.lisp, a function vi-option-value is available:

(import 'lem-vi-mode:vi-option-value)
(setf (vi-option-value "iskeyword") '("@" "_"))

[cxxxr]

Thank you!