Add support implicit conversion between types

[Dicebot]

On Friday, 6 September 2013 at 11:32:11 UTC, Benjamin Thaut wrote:
> Its only a source of troubles in C++ because it is the default 
> behavior. But if you design a library it can make the usage of 
> your api easier and also you have a few more options to stay 
> backwards compatible with your old api.

Probably. But what is the gain? `foo(Foo(5))` looks better than 
`foo(5)` to me in every possible way.

For example, use case that justifies operator overloading 
(despite the danger) in my eyes is ability to replace built-in 
types with custom ones. What is the similar rationale for 
implicit conversion?