🔨 shift NamedContent to plugin interface

docs/source/extensions.rst

@@ -1,7 +1,7 @@
 Extend pyexcel-io Tutorial
 ================================================================================
 
-You are welcome toextend pyexcel-io to read and write more tabular formats.
+You are welcome to extend pyexcel-io to read and write more tabular formats.
 No. 1 rule, your plugin must have a prefix 'pyexcel_' in its module path.
 For example, `pyexcel-xls` has 'pyexcel_xls' as its module path. Otherwise,
 pyexcel-io will not load your plugin.

pyexcel_io/plugin_api/__init__.py

@@ -1,3 +1,3 @@
-from .abstract_sheet import ISheet, ISheetWriter  # noqa: F401
+from .abstract_sheet import ISheet, ISheetWriter, NamedContent  # noqa: F401
 from .abstract_reader import IReader  # noqa: F401
 from .abstract_writer import IWriter  # noqa: F401

pyexcel_io/plugin_api/abstract_sheet.py

@@ -19,3 +19,13 @@ class ISheetWriter(object):
 
     def close(self):
         raise NotImplementedError("How would you close your file")
+
+
+class NamedContent(object):
+    """
+    Helper class for content that does not have a name
+    """
+
+    def __init__(self, name, payload):
+        self.name = name
+        self.payload = payload

pyexcel_io/sheet.py

@@ -10,16 +10,7 @@
 import pyexcel_io.constants as constants
 from pyexcel_io.utils import _index_filter
 from pyexcel_io._compact import irange
-
-
-class NamedContent(object):
-    """
-    Helper class for content that does not have a name
-    """
-
-    def __init__(self, name, payload):
-        self.name = name
-        self.payload = payload
+from pyexcel_io.plugin_api import NamedContent  # noqa: F401
 
 
 class SheetReader(object):