feat: Jump highlight customizations

Closes #27

- Highlight group 'OutlineJumpHighlight' (links to Visual by default)
- Config: outline_window.jump_highlight_duration (integer for
  milliseconds, or boolean to enable/disable)

lua/outline/config.lua

@@ -32,6 +32,7 @@ M.defaults = {
     show_cursorline = true,
     hide_cursor = false,
     winhl = "OutlineDetails:Comment,OutlineLineno:LineNr",
+    jump_highlight_duration = 500,
   },
   preview_window = {
     auto_preview = false,

lua/outline/init.lua

@@ -105,7 +105,17 @@ function M.__goto_location(change_focus)
     M.state.code_win,
     { node.line + 1, node.character }
   )
-  utils.flash_highlight(M.state.code_win, node.line + 1, true)
+
+  if vim.fn.hlexists('OutlineJumpHighlight') == 0 then
+    vim.api.nvim_set_hl(0, 'OutlineJumpHighlight', { link = 'Visual' })
+  end
+  utils.flash_highlight(
+    M.state.code_win,
+    node.line + 1,
+    cfg.o.outline_window.jump_highlight_duration,
+    'OutlineJumpHighlight'
+  )
+
   if change_focus then
     vim.fn.win_gotoid(M.state.code_win)
   end

lua/outline/utils/init.lua

@@ -111,9 +111,12 @@ function M.merge_items_rec(new_node, old_node, index, parent)
 end
 
 function M.flash_highlight(winnr, lnum, durationMs, hl_group)
+  if durationMs == false then
+    return
+  end
   hl_group = hl_group or "Visual"
   if durationMs == true or durationMs == 1 then
-    durationMs = 300
+    durationMs = 500
   end
   local bufnr = vim.api.nvim_win_get_buf(winnr)
   local ns = vim.api.nvim_buf_add_highlight(bufnr, 0, hl_group, lnum - 1, 0, -1)