[RFC] Adding unit test for rlibc

We are pulling in rlibc into Zinc (hackndev/zinc#113), but while reading the code, I though it could do with some unit tests.

So I have added some tests here, but seem like there are a few issues... Please see comments with `XXX` and respond if you have any thoughts :+1:
Right... I see that this crate really mimics how it is in C and even uses `extern "C"`.

I suppose, it would be nice to have something like:
`pub fn rmemset<T>(s: *mut T, c: T, n: uint)`

And then `memset` that mimics C (if it has to exist), will call `rmemset`... This was really the point of this question. I suppose we should have more of a discussion on the list.