encoder: Dump nested tables with their parent

[bochecha]

Currently, we first print all tables at the top level, then all nested
tables at the second level, etc…

As a result, this:

{
    'table1': {
        'foo': 1,
        'nested': {
            'bar': 2,
        },
    },
    'table2': {
        'baz': 3,
    },
}

… gets printed as:

[table1]
foo = 1

[table2]
baz = 3

[table1.nested]
bar = 2

With this commit, we print the nested tables with their parent, so the
same example from above will instead become:

[table1]
foo = 1

[table1.nested]
bar = 2

[table2]
baz = 3

Fixes #88

[bochecha]

In #88, @sayanarijit suggests doing it with a new ordering option

It wasn't clear from that issue whether anything had been decided and that was the way to go, so I figured I wouldn't spend too much time on this before reaching an agreement on this.

As a result, take this pull request as a strawman for how the desired result can be achieved code-wise, and to restart the conversation on what the API should be. 🙂

(Personally, I feel that having the nested tables printed with their parents should be the default, and I can't find any reason not to want that at all)