Faster, leaner implementation of putTime/getTime.

Benchmark on my computer (per call, includes runPut/runGet):

    old putTime: 5658 ns +/- 224ns
    new putTime:  821 ns +/-  24ns (7x faster)

    old getTime: 7228 ns +/- 126ns
    new getTime:   99 ns +/-   4ns (73x faster!!)

Besides, the old format used 25 raw bytes (33.3 bytes on the
base64 output), while the new one uses 8 bytes (10.6 bytes on the
base64 output).
Use a cache for session cookie's expiration time.

The following HelloWorld app was used as benchmark:

  data HelloWorld = HelloWorld
  mkYesod "HelloWorld" [parseRoutes|
    / HomeR GET
  |]

  instance Yesod HelloWorld where
    -- makeSessionBackend = const $ return Nothing

  getHomeR = return . RepPlain . toContent $ "Hello World!"

  main :: IO ()
  main = warp 8080 HelloWorld

The benchmark was tested with httperf under the following
environments:

  [vanilla-nosession] Released yesod-core 1.1.1.1, but without sessions.

  [vanilla-session] Released yesod-core 1.1.1.1 (with sessions).

  [faster-session-1] With patch 065e33a, "Faster, leaner
  implementation of putTime/getTime".

  [faster-session-2] With this commit.

Performance results:

  A) Testing with:
       httperf --hog --client=0/1 --server=localhost \
               --port=8080 --uri=/ --rate=1000 \
               --send-buffer=4096 --recv-buffer=16384 \
               --num-conns=100 --wsess=1000,60,1 \
               --burst-length=20 --session-cookie

     Results:
       vanilla-nosession: 19187.7 req/s (0.1 ms/req)
       vanilla-session:    2523.3 req/s (0.4 ms/req)
       faster-session-1:   2933.5 req/s (0.3 ms/req)
       faster-session-2:   2957.5 req/s (0.3 ms/req)

     This test benchmarks both saving and loading the session.
     Interestingly, this commit provides only a small performance
     increase.

  B) Testing with:
       httperf --hog --client=0/1 --server=localhost \
               --port=8080 --uri=/ --rate=1000 \
               --send-buffer=4096 --recv-buffer=16384 \
               --num-conns=100 --num-calls=1000 \
               --burst-length=20

     Results:
       vanilla-nosession: 43548.7 req/s (0.0 ms/req)
       vanilla-session:    3609.4 req/s (0.3 ms/req)
       faster-session-1:   3454.9 req/s (0.3 ms/req)
       faster-session-2:   3786.9 req/s (0.3 ms/req)

     This test benchmarks only saving the session.  Strangely,
     faster-session-1 was worse than vanilla-session (while
     isolated tests show that the new putTime should be +70x
     faster).  However, there is a non-negligible performance
     increase on faster-session-2.
yesod-test: add support for multiple cookies
yesod-core: generic dispatch instance generation fixes #427 partially.
Check for import changes in Shakespeare files (#413)
Ignore the fay folder (#445)
yesod devel displays "app not loaded" message

In order to achieve this, yesod devel listens on port 3000 and reverse
proxies to port 3001. An environment variable is set to tell the app to
listen on port 3001.
Fixes a spelling mistake.
Merge pull request #447 from dudebout/patch-1

Fixes a spelling mistake.
Merge pull request #440 from piyush-kurur/master

Towards fixing #427 (see also a previous attempt #429)
Allow multiple files (#448)
Merge branch 'rebuild-for-shakespeare'

Conflicts:
	yesod/scaffold/project.cabal.cg
	yesod/yesod.cabal
Switch to project-template
Specify scaffolding via url
Version bumps
refactored mkYesodGeneral to use mkDispatchInstance
Merge branch 'master' of https://github.com/piyush-kurur/yesod
Warning about fork vs resourceForkIO
Added extra explanation from Felipe
Updated scaffold