Fix utf-8 reading in Example 5

Pushing `u8` characters into a `String` is guaranteed to fail with any
non-ascii chars.

Instead, we push into a `Vec<u8>` and then call `from_utf-8()`.

We're still reading the file wrong for every file that isn't utf-8
encoded, but it's still better than nothing.
Merge pull request #49 from hsoft/utf8-fix

Fix utf-8 reading in Example 5