Add WezTerm support

[cpick]

Depends on installing jq, activating WezTerm's shell integration (for the __wezterm_set_user_var() shell function), and placing following snippet in WezTerm's .wezterm.lua:

local wezterm = require 'wezterm'
local config = {}

wezterm.on('user-var-changed', function(window, pane, name, value)
  if name ~= "NOTIFICATION" then
    return
  end

  local notification = wezterm.json_parse(value)

  if notification.check_focus
    and window:is_focused()
    and window:active_pane():pane_id() == pane:pane_id()
  then
    return
  end

  if not notification.timeout_milliseconds then
    notification.timeout_milliseconds = nil
  end

  window:toast_notification(notification.title, notification.message,
    nil, notification.timeout_milliseconds)
end)

return config