feat: Add support for commit_message config variable

This variable can allow you to skip CI pipelines in CI tools like GitLab
CI by adding [CI skip] in the body. There are likely many uses for this
beyond that particular example...

BREAKING CHANGE: If you rely on the commit message to be the version
number only, this will break your code

re #88 #32

docs/configuration.rst

@@ -26,3 +26,6 @@ All configuration described here belongs in ``setup.cfg`` in a section:
     If set to false the pypi uploading will be disabled. This can be useful to create
     tag releases for non-pypi projects.
 
+``commit_message``
+    Long description to append to the version number. This can be useful to skip
+    pipelines in your CI tool

semantic_release/defaults.cfg

@@ -7,3 +7,4 @@ hvcs=github
 commit_parser=semantic_release.history.angular_parser
 upload_to_pypi=true
 version_source=commit
+commit_message=Automatically generated by python-semantic-release

semantic_release/vcs_helpers.py

@@ -80,8 +80,10 @@ def commit_new_version(version):
     :param version: The version number to be used in the commit message
     """
 
+    commit_message = config.get('semantic_release', 'commit_message')
+    message = '{0}\n\n{1}'.format(version, commit_message)
     repo.git.add(config.get('semantic_release', 'version_variable').split(':')[0])
-    return repo.git.commit(m=version, author="semantic-release <semantic-release>")
+    return repo.git.commit(m=message, author="semantic-release <semantic-release>")
 
 
 def tag_new_version(version):

tests/test_vcs_helpers.py

@@ -21,7 +21,10 @@ def test_first_commit_is_not_initial_commit():
 def test_add_and_commit(mock_git):
     commit_new_version('1.0.0')
     mock_git.add.assert_called_once_with('semantic_release/__init__.py')
-    mock_git.commit.assert_called_once_with(m='1.0.0', author="semantic-release <semantic-release>")
+    mock_git.commit.assert_called_once_with(
+        m='1.0.0\n\nAutomatically generated by python-semantic-release',
+        author="semantic-release <semantic-release>"
+    )
 
 
 def test_tag_new_version(mock_git):