Use nose for test

Objective
-------------
For flexible test, `nose` is used for executing all tests.

Details
----------
You can run all tests 

```command
nosetests --with-doctest
```
You can run test of one file

```command
nosetests --with-doctest /path/to/file
```

See help of nostests. You can find some very useful options.

Before trying those command, please install `nose`.

```command
pip install -r requirments.txt
```

or 

```command
pip install nose
```