feat: Add follow_cursor and restore_location

New lua API function: follow_cursor (supports opts.focus_outline).
This sets location in outline to match location in code.

New keymap: restore_location (C-g) by default.
This provides the same functionality as follow_cursor.

I've also refactored other lua API functions for consistency of using
`opts.focus_outline`. If opts is not provided, focus_outline is
defaulted to true. To change this behaviour, set it to false.

lua/symbols-outline/providers/markdown.lua

@@ -17,8 +17,9 @@ function M.hover_info(_, _, on_info)
 end
 
 ---@param on_symbols function
-function M.request_symbols(on_symbols)
-  on_symbols(md_parser.handle_markdown())
+---@param opts table
+function M.request_symbols(on_symbols, opts)
+  on_symbols(md_parser.handle_markdown(), opts)
 end
 
 return M