align columns

Implement http://rosettacode.org/wiki/Align_columns
Sorry for not being clear earlier, in my previous comment I was trying to say that I had changed the function signature to accept a `&str`, and having done that, I was able to get the code to compile and work by making line 3 say `align_columns(text)` instead of `align_columns(text.as_slice())`. My question was, why use `.as_slice()`?