Nested tables in arrays apply their keys to the array table, not its last element

[mattwidmann]

Within an array of tables, a single-bracket table spec with the array's key should apply to its last element (https://github.com/toml-lang/toml#array-of-tables). Instead, lua-toml adds the new table's keys to the array table itself, making it a mixed sequence and associative table.

For example, given the following TOML:

[[people]]
first_name = "Bruce"
last_name = "Springsteen"

[people.birth]
date = "September 23, 1949"
place = "Long Branch, New Jersey"

[people.spouse]
first_name = "Patti"
last_name = "Scialfa"

[[people]]
# an empty element

[[people]]
first_name = "Eric"
last_name = "Clapton"

A parser should produce:

people = {
    {
        first_name = "Bruce", last_name = "Springsteen",
        birth = {
            date = "September 23, 1949",
            place = "Long Branch, New Jersey"
        },
        spouse = { first_name = "Patti", last_name = "Scialfa" },
    }, { -- empty element
    }, {
        first_name = "Eric", last_name = "Clapton"
    }
}

But lua-toml 2.0.1 instead produces:

people = {
    {
        first_name = "Bruce", last_name = "Springsteen"
    }, { -- empty element
    }, {
        first_name = "Eric", last_name = "Clapton"
    },
    birth = {
        date = "September 23, 1949",
        place = "Long Branch, New Jersey"
    },
    spouse = { first_name = "Patti", last_name = "Scialfa" },
}