Spec for #94, in which linking kills capitalisation
Fixes #94; keep case of chunk when linking username

Because `name` and `chunk` can be references to the same object,
the destructive `name.downcase!` also affects `chunk`. This patch
ensures that the two are never the same object, and avoids the
unintended side-effect.
Merge pull request #103 from yaauie/issue-94/username-link-drops-capitalisation

Solution for #94: username link drops capitalisation