Search pyproject.toml in cwd parents. (#71)

* Search pyproject.toml in cwd parents.

* Fix error message when pyproject.toml is not found.

* Attempt to fix Python 2.7 and 3.4 compatibility.

poetry/poetry.py

@@ -45,7 +45,7 @@ class Poetry:
                 fallback=self._config.setting('settings.pypi.fallback', True)
             )
         )
-        
+
     @property
     def file(self):
         return self._file
@@ -68,11 +68,18 @@ class Poetry:
 
     @classmethod
     def create(cls, cwd):  # type: () -> Poetry
-        poetry_file = Path(cwd) / 'pyproject.toml'
+        candidates = [Path(cwd)]
+        candidates.extend(Path(cwd).parents)
+
+        for path in candidates:
+            poetry_file = path / 'pyproject.toml'
+
+            if poetry_file.exists():
+                break
 
-        if not poetry_file.exists():
+        else:
             raise RuntimeError(
-                'Poetry could not find a pyproject.toml file in {}'.format(cwd)
+                'Poetry could not find a pyproject.toml file in {} or its parents'.format(cwd)
             )
 
         local_config = TomlFile(poetry_file.as_posix()).read(True)