Tuple tree parser accepting invalid input

[mischov]

@pclewis recently reported the following problem which indicates that the tuple tree parser wrongly accepts atoms in element attributes.

{"a", [b: "c"], []} |> Meeseeks.parse(:tuple_tree) |> Meeseeks.html()
** (ArgumentError) argument error
    :erlang.iolist_to_binary([[["<", "a", [[" ", :b, "=\"", ["c"], "\""]], ">"], [], ["</", "a", ">"]]])
    (meeseeks) lib/meeseeks/document.ex:80: Meeseeks.Document.html/1

My guess is that this isn't the only case where what is accepted by the tuple tree parser isn't locked down enough.

[mischov]

Fixed in v0.15.0.