* feat: add config option for a tree indent width
add 'indent_width' option to configure visible indent for tree nesting
levels (default is 2).
* add 'bottom' char for a corner extension
* apply stylua formatting
* provide value constraints in documentation
* limit minimal indent width
* make marker symbols have one utf8 char width
* match stylua formatting
* add the commentary regarding utf-8 first symbol match
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