In spec https://github.com/toml-lang/toml#keys
Quoted keys are clarified as
> he exact same rules as either basic strings or literal strings
TOML clearly distinguishes basic string and multi-line basic string
(literal string is also).
https://github.com/toml-lang/toml#string
So table key and quoted key should not allow multi-line basic string
and multi-line literal string.
ABNF definition also describes that.
https://github.com/toml-lang/toml/blob/master/toml.abnf
```
string = ml-basic-string / basic-string / ml-literal-string / literal-string
quoted-key = basic-string / literal-string
```
`string` contains `ml-*` but `quoted-key` doesn't.
This commit completely rewrites this crate from the ground up,
supporting serde at the lowest levels as I believe serde support was
intended to do. This is a major change from the previous versions of
this crate, with a summary of changes being:
* Serialization directly to TOML is now supported without going through
a `Value` first.
* Deserialization directly from TOML is now supported without going
through a `Value`. Note that due to the TOML format some values still
are buffered in intermediate memory, but overall this should be at a
minimum now.
* The API of `Value` was overhauled to match the API of
`serde_json::Value`. The changes here were to:
* Add `is_*` accessors
* Add `get` and `get_mut` for one-field lookups.
* Implement panicking lookups through `Index`
The old `index` methods are now gone in favor of `get` and `Index`
implementations.
* A `Datetime` type has been added to represent a TOML datetime in a
first-class fashion. Currently this type provides no accessors other
than a `Display` implementation, but the idea is that this will grow
support over time for decomposing the date.
* Support for the `rustc-serialize` crate has been dropped, that'll stay
on the 0.2 and 0.1 release trains.
* This crate no longer supports the detection of unused fields, for that though
you can use the `serde_ignored` crate on crates.io
