Add /encoding/utf8 endpoint

Fixes #10 

```
[marca@marca-mac2 ~]$ http :8000/encoding/utf8
HTTP/1.1 200 OK
Access-Control-Allow-Credentials: true
Access-Control-Allow-Origin: *
Connection: close
Content-Length: 14166
Content-Type: text/html; charset=utf-8
Date: Tue, 23 Dec 2014 03:26:46 GMT
Server: gunicorn/19.1.1

<h1>Unicode Demo</h1>

<p>Taken from http://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt</p>

<pre>

UTF-8 encoded sample plain-text file
‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾

Markus Kuhn [ˈmaʳkʊs kuːn] <http://www.cl.cam.ac.uk/~mgk25/> — 2002-07-25


The ASCII compatible UTF-8 encoding used in this plain-text file
is defined in Unicode, ISO 10646-1, and RFC 2279.


Using Unicode/UTF-8, you can write in emails and source code things such as

Mathematics and sciences:

  ∮ E⋅da = Q,  n → ∞, ∑ f(i) = ∏ g(i),      ⎧⎡⎛┌─────┐⎞⎤⎫
                                            ⎪⎢⎜│a²+b³ ⎟⎥⎪
  ∀x∈ℝ: ⌈x⌉ = −⌊−x⌋, α ∧ ¬β = ¬(¬α ∨ β),    ⎪⎢⎜│───── ⎟⎥⎪
                                            ⎪⎢⎜⎷ c₈   ⎟⎥⎪
  ℕ ⊆ ℕ₀ ⊂ ℤ ⊂ ℚ ⊂ ℝ ⊂ ℂ,                   ⎨⎢⎜       ⎟⎥⎬
                                            ⎪⎢⎜ ∞     ⎟⎥⎪
  ⊥ < a ≠ b ≡ c ≤ d ≪ ⊤ ⇒ (⟦A⟧ ⇔ ⟪B⟫),      ⎪⎢⎜ ⎲     ⎟⎥⎪
                                            ⎪⎢⎜ ⎳aⁱ-bⁱ⎟⎥⎪
  2H₂ + O₂ ⇌ 2H₂O, R = 4.7 kΩ, ⌀ 200 mm     ⎩⎣⎝i=1    ⎠⎦⎭

...

Greetings in various languages:

  Hello world, Καλημέρα κόσμε, コンニチハ

Box drawing alignment tests:                                          █
                                                                      ▉
  ╔══╦══╗  ┌──┬──┐  ╭──┬──╮  ╭──┬──╮  ┏━━┳━━┓  ┎┒┏┑   ╷  ╻ ┏┯┓ ┌┰┐    ▊ ╱╲╱╲╳╳╳
  ║┌─╨─┐║  │╔═╧═╗│  │╒═╪═╕│  │╓─╁─╖│  ┃┌─╂─┐┃  ┗╃╄┙  ╶┼╴╺╋╸┠┼┨ ┝╋┥    ▋ ╲╱╲╱╳╳╳
  ║│╲ ╱│║  │║   ║│  ││ │ ││  │║ ┃ ║│  ┃│ ╿ │┃  ┍╅╆┓   ╵  ╹ ┗┷┛ └┸┘    ▌ ╱╲╱╲╳╳╳
  ╠╡ ╳ ╞╣  ├╢   ╟┤  ├┼─┼─┼┤  ├╫─╂─╫┤  ┣┿╾┼╼┿┫  ┕┛┖┚     ┌┄┄┐ ╎ ┏┅┅┓ ┋ ▍ ╲╱╲╱╳╳╳
  ║│╱ ╲│║  │║   ║│  ││ │ ││  │║ ┃ ║│  ┃│ ╽ │┃  ░░▒▒▓▓██ ┊  ┆ ╎ ╏  ┇ ┋ ▎
  ║└─╥─┘║  │╚═╤═╝│  │╘═╪═╛│  │╙─╀─╜│  ┃└─╂─┘┃  ░░▒▒▓▓██ ┊  ┆ ╎ ╏  ┇ ┋ ▏
  ╚══╩══╝  └──┴──┘  ╰──┴──╯  ╰──┴──╯  ┗━━┻━━┛  ▗▄▖▛▀▜   └╌╌┘ ╎ ┗╍╍┛ ┋  ▁▂▃▄▅▆▇█
                                               ▝▀▘▙▄▟

</pre>
```

![screen shot 2014-12-22 at 7 29 33 pm](https://cloud.githubusercontent.com/assets/305268/5534272/f2d1da8a-8a10-11e4-9536-22d88069d951.png)