Experimental support for transit

Added transit as an option (:data-format) to make-channel-socket! (server and client side).

Did some benchmarks to compare edn and transit.

Performed locally on chrome v37 (linux) on an i7-2620m cpu.

Payload: vector of simple maps (size in kb - serialized). Times in ms

| format  | payload | # runs | time  | high | low | avg    |
|---------|---------|--------|-------|------|-----|--------|
| transit | 1024    | 100    | 8409  | 74   | 43  | 57.25  |
| transit | 512     | 100    | 4973  | 62   | 26  | 34.13  |
| transit | 256     | 100    | 3142  | 61   | 16  | 22.93  |
| transit | 128     | 100    | 2379  | 27   | 7   | 15.9   |
| transit | 64      | 100    | 1745  | 24   | 4   | 11.27  |
| transit | 32      | 100    | 1596  | 28   | 3   | 10.05  |
| transit | 8       | 100    | 1671  | 63   | 3   | 12.71  |
| edn     | 1024    | 100    | 66500 | 816  | 534 | 641.69 |
| edn     | 512     | 100    | 34542 | 465  | 267 | 332.72 |
| edn     | 256     | 100    | 15065 | 246  | 89  | 143.04 |
| edn     | 128     | 100    | 8586  | 150  | 63  | 81.84  |
| edn     | 64      | 100    | 4642  | 79   | 35  | 44.09  |
| edn     | 32      | 100    | 3182  | 57   | 20  | 30.13  |
| edn     | 8       | 100    | 2017  | 48   | 6   | 16.53  |