Add link to doc in NEWS/MIGRATING for Modules 4.0>4.4

[xdelaruelle]

In the NEWS and MIGRATING documents, there is no hypertext link to the documentation for the changes description of Modules releases between 4.0.0 and 4.4.1.

Both documents could be edited to update the changes description for releases between 4.0.0 and 4.4.1 and use the Sphinx reStructuredText keywords to set links to the documentation. It applies to:

• environment variables: use Sphinx object envvar
• installation option: use Sphinx object instopt
• module configuration option: use Sphinx object mconfig
• module command option: use Sphinx object option
• module sub-command: use Sphinx object subcmd
• modulefile command: use Sphinx object mfcmd
• modulefile variable: use Sphinx object mfvar

Example syntax to use a Sphinx object:

:object:`ref`

For instance:

:envvar:`MODULES_CMD`