Build of path is not safe

[jbuisine]

In this code example: https://github.com/prise-3d/rawls_api/blob/devel/api.py#L41, the path construction is not safe.

Package os gives the possibility to build path in a safe way.

Example:

import os
global_path = 'projects'
csv_path = os.path.join(global_path, 'data', 'csv_data')

This issue can be linked with issue #2.