MAINT: Update towncrier version in install and notes

We were installing towncrier from the github master branch because there
had been no releases with the needed fixes. That has changed with the
recent release of versions 19.9.0 and 21.3.0.

Author: charris

Diff for: .circleci/config.yml

@@ -40,7 +40,7 @@ jobs:
           name: create release notes
           command: |
             . venv/bin/activate
-            pip install git+https://github.com/hawkowl/towncrier.git@master
+            pip install towncrier
             VERSION=$(python -c "import setup; print(setup.VERSION)")
             towncrier build --version $VERSION --yes
             ./tools/ci/test_all_newsfragments_used.py

Diff for: doc/HOWTO_RELEASE.rst.txt

@@ -258,10 +258,8 @@ Check the release notes
 Use `towncrier`_ to build the release note and
 commit the changes. This will remove all the fragments from
 ``doc/release/upcoming_changes`` and add ``doc/release/<version>-note.rst``.
-Note that currently towncrier must be installed from its master branch as the
-last release (19.2.0) is outdated.
 
-    towncrier --version "<version>"
+    towncrier build --version "<version>"
     git commit -m"Create release note"
 
 Check that the release notes are up-to-date.
@@ -275,7 +273,7 @@ following:
   - for SciPy, supported NumPy version(s)
   - outlook for the near future
 
-.. _towncrier: https://github.com/hawkowl/towncrier
+.. _towncrier: https://pypi.org/project/towncrier/
 
 
 Update the release status and create a release "tag"

Diff for: release_requirements.txt

@@ -14,4 +14,4 @@ twine
 
 # building and notes
 Paver
-git+https://github.com/hawkowl/towncrier.git@master
+towncrier