Convert readthedocs links for their .org -> .io migration for hosted projects

CONTRIBUTING.md

@@ -2,6 +2,6 @@
 
 We're thrilled you want to contribute to nbgrader.
 
-The [developer documentation](https://nbgrader.readthedocs.org/en/latest/contributor_guide/overview.html)
+The [developer documentation](https://nbgrader.readthedocs.io/en/latest/contributor_guide/overview.html)
 gives an overview of how various parts of the project work and what our
 expectations are for contributions.

README.md

@@ -6,7 +6,7 @@
 
 A system for assigning and grading Jupyter notebooks.
 
-[Documentation can be found on Read the Docs.](http://nbgrader.readthedocs.org)
+[Documentation can be found on Read the Docs.](https://nbgrader.readthedocs.io)
 
 
 ## Highlights of nbgrader
@@ -24,7 +24,7 @@ submit, and validate their assignments.
 ![nbgrader assignment list](nbgrader/docs/source/user_guide/images/student_assignment.gif "nbgrader assignment list")
 
 ### The command line tools of nbgrader
-[Command line tools](https://nbgrader.readthedocs.org/en/latest/command_line_tools/index.html)
+[Command line tools](https://nbgrader.readthedocs.io/en/latest/command_line_tools/index.html)
 offer an efficient way for the instructor to generate, assign, release, collect,
 and grade notebooks.
 
@@ -39,12 +39,12 @@ Or, if you use [Anaconda](https://www.continuum.io/downloads):
     conda install -c jhamrick nbgrader
 
 For detailed instructions on installing nbgrader and the nbgrader extensions
-for Jupyter notebook, please see [Installation](https://nbgrader.readthedocs.org/en/latest/user_guide/installation.html)
+for Jupyter notebook, please see [Installation](https://nbgrader.readthedocs.io/en/latest/user_guide/installation.html)
 section in the User Guide.
 
 
 ## Contributing
-Please see the [contributing guidelines and documentation](https://nbgrader.readthedocs.org/en/latest/contributor_guide/overview.html).
+Please see the [contributing guidelines and documentation](https://nbgrader.readthedocs.io/en/latest/contributor_guide/overview.html).
 
 If you want to develop features for nbgrader, please follow the
-[development installation instructions](https://nbgrader.readthedocs.org/en/latest/contributor_guide/installation_developer.html).
+[development installation instructions](https://nbgrader.readthedocs.io/en/latest/contributor_guide/installation_developer.html).

nbgrader/apps/quickstartapp.py

@@ -144,7 +144,7 @@ def start(self):
 
                 For further details, please see the full nbgrader documentation at:
 
-                    http://nbgrader.readthedocs.org/
+                    https://nbgrader.readthedocs.io/
                 """
             ).lstrip(),
             course_path,

nbgrader/docs/source/configuration/jupyterhub_config.rst

@@ -18,7 +18,7 @@ Using nbgrader with JupyterHub
     :doc:`/user_guide/philosophy`
         More details on how the nbgrader hierarchy is structured.
 
-    `JupyterHub Documentation <http://jupyterhub.readthedocs.org/en/latest/getting-started.html>`_
+    `JupyterHub Documentation <https://jupyterhub.readthedocs.io/en/latest/getting-started.html>`_
         Detailed documentation describing how JupyterHub works, which is very
         much required reading if you want to integrate the formgrader with
         JupyterHub.

nbgrader/docs/source/contributor_guide/documentation.rst

@@ -35,7 +35,7 @@ executed, please make sure you re-run all the documentation before committing.
 While the documentation gets built automatically on Read The Docs, the notebooks do **not** get execute by Read The Docs -- they must be executed manually.
 However, executing the notebooks is easy to do!
 
-Our docs are built with `nbconvert <http://nbconvert.readthedocs.org/en/latest/>`_,
+Our docs are built with `nbconvert <https://nbconvert.readthedocs.io/en/latest/>`_,
 `Pandoc <http://pandoc.org/>`_, and `Sphinx <http://sphinx-doc.org/>`_.
 To build the docs locally, run the following command::
 
@@ -60,4 +60,4 @@ Automatic builds
 ----------------
 When a commit is made on the ``master`` branch, documentation is automatically
 built by Read The Docs and rendered at
-`nbgrader.readthedocs.org <http://nbgrader.readthedocs.org>`_.
+`nbgrader.readthedocs.org <https://nbgrader.readthedocs.io>`_.

nbgrader/docs/source/user_guide/advanced.rst

@@ -130,7 +130,7 @@ example:
 
     c.Exporter.preprocessors = ['nbgrader.preprocessors.ClearSolutions']
 
-See also the nbconvert docs on `custom preprocessors <http://nbconvert.readthedocs.io/en/latest/nbconvert_library.html#Custom-Preprocessors>`__.
+See also the nbconvert docs on `custom preprocessors <https://nbconvert.readthedocs.io/en/latest/nbconvert_library.html#Custom-Preprocessors>`__.
 
 Calling nbgrader apps from Python
 ---------------------------------