Add constructors for generated types.

Currently, the only way to create generated types is to use the object initializer syntax (or at least that's what its called in C#). Instead, we should provide a constructor as well to cut down the verbosity.

Currently we have: 
```rust
improbable::Coordinates { 
	x: 0.0, 
	y: 0.0, 
	z: 0.0 
}
```

where we could have: 
```rust
improbable::Coordinates::new(0.0, 0.0, 0.0)
```