move the extra menus of Nushell into custom-menus/extra/ (#550)

* add the extra menus in `custom-menus/extra/`

* add some notes about how to use the extra menus in bindings

custom-menus/extra/commands.nu

@@ -0,0 +1,30 @@
+# can be used in the REPL by adding something like the following block to `$env.config.keybindings` in your `config.nu`
+# {
+#     name: commands_menu
+#     modifier: control
+#     keycode: char_t
+#     mode: [emacs, vi_normal, vi_insert]
+#     event: { send: menu name: commands_menu }
+# }
+
+{
+    name: commands_menu
+    only_buffer_difference: false
+    marker: "# "
+    type: {
+        layout: columnar
+        columns: 4
+        col_width: 20
+        col_padding: 2
+    }
+    style: {
+        text: green
+        selected_text: green_reverse
+        description_text: yellow
+    }
+    source: { |buffer, position|
+        scope commands
+        | where name =~ $buffer
+        | each { |it| {value: $it.name description: $it.usage} }
+    }
+}

custom-menus/extra/commands_with_description.nu

@@ -0,0 +1,32 @@
+# can be used in the REPL by adding something like the following block to `$env.config.keybindings` in your `config.nu`
+# {
+#     name: commands_with_description_menu
+#     modifier: control
+#     keycode: char_s
+#     mode: [emacs, vi_normal, vi_insert]
+#     event: { send: menu name: commands_with_description }
+# }
+
+{
+    name: commands_with_description_menu
+    only_buffer_difference: true
+    marker: "# "
+    type: {
+        layout: description
+        columns: 4
+        col_width: 20
+        col_padding: 2
+        selection_rows: 4
+        description_rows: 10
+    }
+    style: {
+        text: green
+        selected_text: green_reverse
+        description_text: yellow
+    }
+    source: { |buffer, position|
+        scope commands
+        | where name =~ $buffer
+        | each { |it| {value: $it.name description: $it.usage} }
+    }
+}

custom-menus/extra/vars.nu

@@ -0,0 +1,29 @@
+# can be used in the REPL by adding something like the following block to `$env.config.keybindings` in your `config.nu`
+# {
+#     name: vars_menu
+#     modifier: alt
+#     keycode: char_o
+#     mode: [emacs, vi_normal, vi_insert]
+#     event: { send: menu name: vars_menu }
+# }
+
+{
+    name: vars_menu
+    only_buffer_difference: true
+    marker: "# "
+    type: {
+        layout: list
+        page_size: 10
+    }
+    style: {
+        text: green
+        selected_text: green_reverse
+        description_text: yellow
+    }
+    source: { |buffer, position|
+        scope variables
+        | where name =~ $buffer
+        | sort-by name
+        | each { |it| {value: $it.name description: $it.type} }
+    }
+}