Readme: fix external docs/build links

* The default (GitHub) readme should point
  to the stable docs version, rather than
  the latest development version.
* The frozen links in PyPI should use the full
  patch version number (X.Y.Z), not just the minor
  X.Y version. (Leftover from Djrill's branch-based
  version management; Anymail uses tags
  for versions, and old way was creating incorrect
  frozen doc links for patch releases.)

README.rst

@@ -57,13 +57,14 @@ Anymail releases follow `semantic versioning <http://semver.org/>`_.
        :target: https://travis-ci.org/anymail/django-anymail
        :alt:    build status on Travis-CI
 
-.. image:: https://readthedocs.org/projects/anymail/badge/?version=latest
-       :target: https://anymail.readthedocs.io/en/latest/
+.. image:: https://readthedocs.org/projects/anymail/badge/?version=stable
+       :target: https://anymail.readthedocs.io/en/stable/
        :alt:    documentation on ReadTheDocs
 
 **Resources**
 
-* Full documentation: https://anymail.readthedocs.io/en/latest/
+* Full documentation: https://anymail.readthedocs.io/en/stable/
+  (`development version <https://anymail.readthedocs.io/en/latest/>`_)
 * Package on PyPI: https://pypi.python.org/pypi/django-anymail
 * Project on Github: https://github.com/anymail/django-anymail
 
@@ -151,5 +152,5 @@ or SparkPost or any other supported ESP where you see "mailgun":
 .. END quickstart
 
 
-See the `full documentation <https://anymail.readthedocs.io/en/latest/>`_
+See the `full documentation <https://anymail.readthedocs.io/en/stable/>`_
 for more features and options.

setup.py

@@ -11,12 +11,12 @@ with open("anymail/_version.py") as f:
 
 
 def long_description_from_readme(rst):
-    # Freeze external links to refer to this X.Y version (on PyPI).
-    # (This relies on tagging or branching releases with 'vX.Y' in GitHub.)
-    release = 'v%s' % __minor_version__  # vX.Y
-    rst = re.sub(r'(?<=branch=)master'     # Travis build status: branch=master --> branch=vX.Y
-                 r'|(?<=/)latest'          # ReadTheDocs links: /latest --> /vX.Y
-                 r'|(?<=version=)latest',  # ReadTheDocs badge: version=latest --> version=vX.Y
+    # Freeze external links (on PyPI) to refer to this X.Y or X.Y.Z tag.
+    # (This relies on tagging releases with 'vX.Y' or 'vX.Y.Z' in GitHub.)
+    release = 'v%s' % __version__  # vX.Y or vX.Y.Z
+    rst = re.sub(r'(?<=branch=)master'     # Travis build status: branch=master --> branch=vX.Y.Z
+                 r'|(?<=/)stable'          # ReadTheDocs links: /stable --> /vX.Y.Z
+                 r'|(?<=version=)stable',  # ReadTheDocs badge: version=stable --> version=vX.Y.Z
                  release, rst)  # (?<=...) is "positive lookbehind": must be there, but won't get replaced
     return rst