Reformat test to be more idiomatic

Should not usually have to def anything inside a test, and
clojure.test/are gives us the same parameterized test behavior.
Use streams instead of string concatenation

This should allow seamless use of the middleware even for large
response bodies.
Don't reinvent clojure.lang.SeqEnumeration

I expected to find something like this in clojure.core, but didn't see
it because it was merely a class rather than a var I could find in the
namespace. Now I know better.
Merge pull request #3 from fredericksgary/master

Use streams instead of string concatenation