build: issue2551397: remove support for python 3.6

3.7 ci build works. Make changes to make 3.7 current minimum supported
version. Also removed some references that apply only when running
under 2.7.

Author: rouilj

doc/announcement.txt

@@ -117,12 +117,12 @@ all your trackers to update the database schema version. Do
 this before you use the web, command-line or mail interface
 and before any users access the tracker.
 
-Roundup requires Python 2 newer than version 2.7.12 or Python 3
-newer than or equal to version 3.6 for correct operation. (Python
-3.4 or 3.5 may work, but are not tested.) Note that Roundup 2.4.0
-will be the last release to support Python 2. You should deploy
-new trackers with Python 3 and plan on upgrading older trackers
-from Python 2 to Python 3. See the upgrade guide.
+Roundup requires Python 3 newer than or equal to version 3.7 for
+correct operation. (Python 3.4 or 3.5, or 3.6 may work, but are not
+tested.) Note that Roundup 2.4.0 was the last release to support
+Python 2. You should deploy new trackers with Python 3 and plan on
+upgrading older trackers from Python 2 to Python 3. See the upgrade
+guide.
 
 To give Roundup a try, just download (directions above),
 unpack and run::
@@ -164,7 +164,7 @@ The system facilitates communication among the participants
 by managing discussions and notifying interested parties
 when issues are edited. One of the major design goals for
 Roundup that it be simple to get going. Roundup is therefore
-usable "out of the box" with any Python 3.6+
+usable "out of the box" with any Python 3.7+
 installation. It doesn't even need to be "installed" to be
 operational, though an install script is provided.
 

doc/installation.txt

@@ -178,7 +178,7 @@ can remove the tracker using ``rm -f`` on the ``demo`` directory.
 Prerequisites
 =============
 
-Roundup requires Python 2.7 [3]_ or 3.6 or newer with a functioning anydbm
+Roundup requires Python 3.7 or newer with a functioning anydbm
 or sqlite module. The version installed by most vendors should work if
 it meets the version requirements. If necessary, you can download the
 latest version from https://www.python.org/. It is highly recommended
@@ -318,9 +318,6 @@ requests
 .. _Using Redis for Session Databases:
    admin_guide.html#using-redis-for-session-databases
 
-.. [3] Do not use Python 2 for new installs. The next minor release
-       (2.5.0 expected summer 2025) will drop support for Python 2.
-
 Installing Roundup
 ==================
 

doc/tracker_templates.txt

@@ -5,7 +5,7 @@ Roundup Tracker Templates
 The templates distributed with Roundup are stored in the "share" directory
 nominated by Python. On Unix this is typically
 ``/usr/share/roundup/templates/`` (or ``/usr/local/share...``) and
-on Windows this is ``c:\python27\share\roundup\templates\``.
+on Windows this is ``c:\python38\share\roundup\templates\``.
 
 The template loading looks in four places to find the templates:
 
@@ -17,9 +17,9 @@ The template loading looks in four places to find the templates:
    `sys.base_prefix/local``. This finds templates (and locales)
    installed by pip. E.G. in a virtualenv located at (``sys.prefix``):
    ``/tools/roundup``, roundup would be at:
-   ``/tools/roundup/lib/python3.6/site-packages/roundup``. The
+   ``/tools/roundup/lib/python3.7/site-packages/roundup``. The
    templates would be at:
-   ``/tools/roundup/lib/python3.6/site-packages/tools/roundup/share/roundup/templates/``.
+   ``/tools/roundup/lib/python3.7/site-packages/tools/roundup/share/roundup/templates/``. (Replace 3.7 with the Python version you are running.)
 3. ``<roundup.admin.__file__>/../../share/roundup/templates/*``.
    This will be used if Roundup's run in the distro (aka. source)
    directory.

setup.py

@@ -245,7 +245,6 @@ def main():
                        'Programming Language :: Python :: 2',
                        'Programming Language :: Python :: 2.7',
                        'Programming Language :: Python :: 3',
-                       'Programming Language :: Python :: 3.6',
                        'Programming Language :: Python :: 3.7',
                        'Programming Language :: Python :: 3.8',
                        'Programming Language :: Python :: 3.9',