why is `base_path` needed ? It seems that path is always a full path so `base_path` should be equal to `os.path.dirname(path)`.
```
> /home/simon/Dev/pelican/pelican/readers.py(347)read_file()
    346 
--> 347     path = os.path.abspath(os.path.join(base_path, path))
    348     source_path = os.path.relpath(path, base_path)

ipdb> base_path
u'/home/simon/Dev/pelican/samples/content'
ipdb> path
u'/home/simon/Dev/pelican/samples/content/article2-fr.rst'
```