feat(renderer): add renderer.indent_width (#1505)

* 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

doc/nvim-tree-lua.txt

@@ -213,6 +213,7 @@ Subsequent calls to setup will replace the previous configuration.
         full_name = false,
         highlight_opened_files = "none",
         root_folder_modifier = ":~",
+        indent_width = 2,
         indent_markers = {
           enable = false,
           inline_arrows = true,
@@ -220,6 +221,7 @@ Subsequent calls to setup will replace the previous configuration.
             corner = "└",
             edge = "│",
             item = "│",
+            bottom = "─",
             none = " ",
           },
         },
@@ -709,6 +711,10 @@ UI rendering setup
     available options.
       Type: `string`, Default: `":~"`
 
+    *nvim-tree.renderer.indent_width*
+    Number of spaces for an each tree nesting level. Minimum 1.
+      Type: `number`, Default: `2`
+
     *nvim-tree.renderer.indent_markers*
     Configuration options for tree indent markers.
 
@@ -722,8 +728,8 @@ UI rendering setup
           Type: `boolean`, Default: `true`
 
         *nvim-tree.renderer.indent_markers.icons*
-        Icons shown before the file/directory.
-          Type: `table`, Default: `{ corner = "└", edge = "│", item = "│", none = " ", }`
+        Icons shown before the file/directory. Length 1.
+          Type: `table`, Default: `{ corner = "└", edge = "│", item = "│", bottom = "─", none = " ", }`
 
     *nvim-tree.renderer.icons*
     Configuration options for icons.