Add unittesting

Add basic unit test. 

It can be run with:
```
python tests/test_pydealer.py
```
Or directly with setup (this will install the package):
```
python setup.py test
```

I added some basic unittest with covers 84% of the code. 

It will be great if you can setup travis-ci (it's free for opensource projects) in order to automatically build test each commit and each pull request. 

Here are some steps:

http://docs.travis-ci.com/user/getting-started/ and http://docs.travis-ci.com/user/languages/python/

Basically you must add a .travis.yml file with the following content:

```
language: python
python:
  - "2.6"
  - "2.7"
  - "3.3"
  - "3.4"
script:
  - python setup.py test
```
Feel free to modify the versions you want to support.