[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.

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.

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。）