[core.config] Make `parse_app_arg' a NOOP for tables.
[META] Use `core.config.parse_app_arg' uniformly.
[META] Refrain from using `([[{...}]]):format(...)' constructs
and use table literals instead.
[core.config] Remove type checking of `arg' in `config.app()'.
(It's done in `parse_app_arg'.)
Merge pull request #293 from eugeneia/app-table-args

Table app args refactoring
[keyed_ipv6_tunnel] Fix regression introduced by #293: `Table app args
refactoring'.
Merge pull request #308 from eugeneia/fix-tunnel-regression

[keyed_ipv6_tunnel] Fix regression introduced by #293 URGENT