Implement `InfluxDbReadable` and `InfluxDbWriteable` procedural macros

[Empty2k12]

Right now, to save an object to InfluxDb, you need to add each field individually to a query like so

#[derive(Deserialize, InfluxDbWriteable)]
struct Humidity {
    time: i32,
    humidity: i32,
}

let measurement = Humidity {
    time: 11,
    humidity: 1,
}
let write_query = InfluxDbQuery::write_query(Timestamp::HOURS(&measurement.time), "humidity")
    .add_field("humidity", &measurement.humidity);

This should be easily inferable by a procedural macro so that there could be a new function like

let write_query = InfluxDbQuery::write_query(&humidity);

[msrd0]

#23