[Releated:#17] Add PrimitiveType to PrimitiveType Conversion Method

Swift Current Version don't has some Primitive to Primitive Conversion.
(e.g. Int32 to Int, Int16 to Int,CChar64 to String...)

So, Add Conversion Methods.

```swift
it("primitive types") {
    var a: CInt = 1
    expect(a).to.equal(1) // No Warning, No error. :)
}
```

Known Issue.
Currently, There are not Library Management tool for Swift.
This PullRequest Code has possibility of "dupplicate error".

For example,
Someone write above code.

```swift
extension UInt8{
    // dupplicate error :(
    @conversion func __conversion() -> (UInt){
        return UInt(self)
    }
}    
```

When we are able to use Cocoapods for Swift, This Code should be deleted.
（もしCocoapodでSwiftが使えるようになったらこのコードは消しましょう。）