Finish implementation

src/default.md.j2

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+## Coverage report
+{% if previous_coverage -%}
+The coverage rate went from `{{ previous_coverage }}%` to `{{ coverage }}%` {{
+    ":arrow_up:" if previous_coverage < coverage else
+    ":arrow_down:" if previous_coverage > coverage else
+    ":arrow_right:"
+}}
+{%- else -%}
+The coverage rate is `{{ coverage }}%`
+{%- endif %}
+
+{% if branch_coverage -%}
+The branch rate is `{{ branch_coverage }}%`
+{%- endif %}
+
+`{{ diff_coverage }}%` of new lines are covered.
+
+{%if file_info -%}
+<details>
+<summary>Diff Coverage details (click to unfold)</summary>
+
+{% for filename, stats in file_info.items() -%}}
+### {{ filename }}
+`{{ stats.diff_coverage }}%` of new lines are covered
+
+{%- endfor %}
+{%- endif -%}
+</details>
+{{ marker }}