Feat: Displayer now supports highlights for separator and elements (#304)

Separator Example: When creating the displayer
```lua
local displayer = entry_display.create {
  separator = " ",
  separator_hl = 'Visual', -- New
  items = {
    { width = opts.bufnr_width },
    { width = 4 },
    { remaining = true },
  },
}
```

Elements Example: When submitting data
```lua
local hl_group = x == y then 'Normal' or 'Visual'

return displayer {
  entry.bufnr,
  { entry.indicator, hl_group },
  display_bufname .. ":" .. entry.lnum,
}
```

0 files changed, 0 insertions, 0 deletions