Caches articles

Output: `ab -n 3000 -c 5 -k http://127.0.0.1:8080/2013-9-9-a-blog-post`

Before:

    Requests per second:    1641.15 [#/sec] (mean)
    Time per request:       3.047 [ms] (mean)
    Time per request:       0.609 [ms] (mean, across all concurrent requests)
    Transfer rate:          1854.31 [Kbytes/sec] received

After:

    Requests per second:    2004.00 [#/sec] (mean)
    Time per request:       2.495 [ms] (mean)
    Time per request:       0.499 [ms] (mean, across all concurrent requests)
    Transfer rate:          2264.29 [Kbytes/sec] received