We've been using this default already in `normalize_tag`,
but setting this value in the settings dict is cleaner.

config_path and changelog_path rely on the modified CWD provided by
tmp_commitizen_project, so they should use this fixture.

Closes #519

CLI flag name: --tag-regex

Heavily inspired by
#537, but extends
it with a smart default value to exclude non-release tags. This was
suggested in
#519 (comment)

This allows monorepo support as long as projects are organized within
subdirectories.

Under the following conditions:
- commit_parser either does not have a capture group for change_type or
  change_type is None for other reasons
- change_type_map is provided

We get the following error:
```
TypeError: argument of type 'NoneType' is not iterable
```

This provides a default change_type which can also be mapped using the
change_type_map.

Setting changelog_ignore_body to true will ignore the body of the commit
message when processing commits for the changelog.

This mostly poses an issue for breaking changes, which may provide additional
details in the body. With this flag set to true, only the subject of the commit
message is processed.