Adapted to ipv6-enabled tox

main.c:
- init_tox(): tox_new() => tox_new(TOX_ENABLE_IPV6_DEFAULT) (enables dual-stack per default)
- resolv_addr(): killed
- init_connection(): use tox_bootstrap_from_address(), which does the resolving

prompt.c:
- cmd_connect(): use tox_bootstrap_from_address(), which does the resolving