To support JS expansions the parser needs to be taught how to run async tasks.

async wrappers

• async wrapper of uzbl_commands_parse
• async wrapper of uzbl_variables_expand

use uzbl_commands_run_async where possible

• chain command
• include command
• spawn command
• gui - destroy cb
• gui - run menu command
• main - default config
• main - read config file
• variables - expand js
• variables - expand uzbl
• variables - expand sh
• io - commands from socket/fifo