Add setup script with keeping directory structure

[yxhamada]

With using previous pull request #9 as a reference, added different type of setup script without changing current directory structure.

[hootnot]

I agree that this code should be pip installable. Pull request #9 altered the directory structure to a structure that complies with https://pythonhosted.org/an_example_pypi_project/setuptools.html . This structure allows adding unittest also.

I too had the problem with automated deployment to install the oandapy module using Ansible for my own project: oanda-trading-environment , which is pip installable from pypi: https://pypi.python.org/pypi/oanda-trading-environment/0.2.0.

The current repository does not allow to install oandapy using pip.

For this I altered the structure in a way like pull request #9 and Ansible installs oandapy from my fork with its own version number, which is not desirable.
I did not do a pull request again since request #9 wasn't merged. But I would like to see the change also, so the code can be installed as a module from the original repo with versioning controlled there.
I will make a pull request for the changes I made. This includes also the change in directory structure.

After this change installing and upgrading comes down to:
pip install git+https://github.com/oanda/oandapy

a pypi package would even be more convenient:
pip install oandapy