Allow both Option=! and Option=WrappedType for optional fields

[RustyNova016]

Currently, you need to choose between whether giving an Option or a value for optional fields. But sometimes, it's easier to give an option to a builder, and others a value.

It would be great to have a Builder::field_optional() function when using Option=WrappedType that takes in a Option, allowing for both styles depending on the use of the builder

[loganmzz]

Sounds good.

I may also add a setting (to be defined) when set makes available following functions:

// Named
fn field<T: Into<X>>(value: Option<T>) {}
fn field_some<T: Into<X>>(value: T) {}
fn field_none() {}

// Tuple - Unordered
fn set0<T: Into<X>>(value: Option<T>) {}
fn set0_some<T: Into<X>>(value: T) {}
fn set0_none() {}

// Tuple - Ordered
fn set<T: Into<X>>(value: Option<T>) {}
fn some<T: Into<X>>(value: T) {}
fn none() {}

As I'm giving a talk (about Rust btw :) ) next week, I won't have time to take a look until next week-end.

[loganmzz]

@RustyNova016 Sorry for the delay, I have released 1.3.0, but without setting to reverse optional setters (Option by default and field_some() for wrapped type)

[RustyNova016]

Neat! Thanks.