toml-datetime-compat

Adds a functionality to easily convert between toml_datetime's and chrono's/time's types.

Both with the serde derive macros:

```rust

[derive(Deserialize, Serialize)]

struct SomeDateTimes { #[serde(with = "tomldatetimecompat")] chrononaivedate: chrono::NaiveDate, #[serde(with = "tomldatetimecompat")] chrononaivetime: chrono::NaiveTime, #[serde(with = "tomldatetimecompat")] chrononaivedatetime: chrono::NaiveDateTime, #[serde(with = "tomldatetimecompat")] chronodatetimeutc: chrono::DateTime, #[serde(with = "tomldatetimecompat")] chronodatetimeoffset: chrono::DateTime, #[serde(with = "tomldatetimecompat")] timedate: time::Date, #[serde(with = "tomldatetimecompat")] timetime: time::Time, #[serde(with = "tomldatetimecompat")] timeprimitivedatetime: time::PrimitiveDateTime, #[serde(with = "tomldatetimecompat")] timeoffsetdate_time: time::OffsetDateTime,"# } ```

And by introducing a new trait ToFromToml that adds to_toml and from_toml functions to the relevant structs from chrono and time.