Path loader binding

>>> from woger import BasePathStructure, Bind, Workspace
>>> import tempfile
>>>
>>> content = 'Example of binding'
>>>
>>> def create_example_txt(path, ws_root, action):
...     ws = Workspace.construct(ws_root)
...     with ws.track(action):
...         print('Creating example.txt...')
...         with open(str(path), 'w') as f:
...             f.write(content)
...     return True
...
>>>
>>> class PathStructure(BasePathStructure):
...     example = Bind('example.txt', create_example_txt)
...
>>>
>>> with tempfile.TemporaryDirectory() as root:
...     ps = Workspace.construct(root, PathStructure).path
...
...     with open(str(ps.example), 'r') as f:
...         print(f.read())
...
Creating example.txt...
Example of binding