docs: set up python-semantic-release templates (#21)

Fixes #3

.github/templates/.changes.j2

@@ -0,0 +1,16 @@
+{%- set commit_type_heading_mapping = (
+  ("breaking", "Breaking Changes"),
+  ("feature", "Features"),
+  ("fix", "Bug Fixes"),
+  ("performance", "Performance improvements"),
+  ("refactor", "Code Refactoring"),
+  ("test", "Testing"),
+  ("documentation", "Documentation"),
+) -%}
+
+{% for commit_type, heading in commit_type_heading_mapping if commit_type in release["elements"] %}
+### {{ heading }}
+
+{% for commit in release["elements"][commit_type] -%}
+- {% if commit.scope %}**{{ commit.scope }}:** {% endif %}{{ commit.descriptions[0] }} ([`{{ commit.short_hash }}`]({{ commit.hexsha|commit_hash_url }}))
+{% endfor %}{% endfor %}

.github/templates/.release_notes.md.j2

@@ -0,0 +1,4 @@
+{%- set releases = context.history.released.items() | list -%}
+{%- set prev_version = releases[1][0] -%}
+{% include ".changes.j2" %}
+{{ "**Full Changelog**: (%s)" | format(prev_version | compare_url(version)) }}

.github/templates/CHANGELOG.md.j2

@@ -0,0 +1,21 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html). See
+[conventional commits](https://www.conventionalcommits.org/en/v1.0.0/) for commit guidelines.
+
+{# UNRELEASED -#}
+{% set last_release = context.history.released.items() | first | first -%}
+## {{ "[Unreleased](%s)" | format(last_release.as_tag() | compare_url("main")) }}
+
+{# RELEASED -#}
+{% for version, release in context.history.released.items() -%}
+{%- if loop.nextitem -%}
+{%- set compare_url_ = loop.nextitem[0] | compare_url(version) -%}
+## [{{ version.as_tag() }}]({{ compare_url_ }}) ({{ release.tagged_date.strftime("%Y-%m-%d") }})
+{% else -%}
+## {{ version.as_tag() }} ({{ release.tagged_date.strftime("%Y-%m-%d") }})
+{% endif -%}
+{% include ".changes.j2" %}
+{%- endfor -%}