Make JIRA links really easily

Now you can make JIRA links like this:
```
    :jira:`TNL-4904`
```

Author: Ned Batchelder

en_us/release_notes/source/2016/lms/lms_0516_2016.rst

@@ -29,6 +29,6 @@
 
 * A UTF-8 character encoding error that prevented some course teams from
   downloading the CSV file of certificates issued on the instructor dashboard
-  has been corrected. (CRI-57)
+  has been corrected. (:jira:`CRI-57`)
 
 .. _XSeries Programs Page: https://partners.edx.org/announcements/coming-soon-xseries-programs-page

shared/conf.py

@@ -24,7 +24,16 @@
 
 # Add any Sphinx extension module names here, as strings. They can be extensions
 # coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
-extensions = ['sphinx.ext.autodoc', 'sphinx.ext.doctest', 'sphinx.ext.intersphinx', 'sphinx.ext.coverage', 'sphinx.ext.pngmath', 'sphinx.ext.mathjax', 'sphinx.ext.ifconfig']
+extensions = [
+    'sphinx.ext.autodoc',
+    'sphinx.ext.doctest',
+    'sphinx.ext.intersphinx',
+    'sphinx.ext.coverage',
+    'sphinx.ext.pngmath',
+    'sphinx.ext.mathjax',
+    'sphinx.ext.ifconfig',
+    'sphinx.ext.extlinks',
+]
 
 # The suffix of source filenames.
 source_suffix = '.rst'
@@ -111,3 +120,8 @@ def feedback_form_url(project, page):
     'partnerreleasenotes': ('http://edx.readthedocs.org/projects/edx-release-notes/en/latest/', None),
     '2014releasenotes' : ('http://edx.readthedocs.org/projects/edx-2013-2014-release-notes/en/latest/', None)
 }
+
+extlinks = {
+    # :jira:`TNL-4904` becomes: <a href='https://openedx.atlassian.net/browse/TNL-4904'>TNL-4904</a>
+    'jira': ('https://openedx.atlassian.net/browse/%s', ''),
+}