Support using a template for `quickblog new`#87

When creating a new post, I would like to have it look something like this: ``` markdown Title: Test Date: 2024-01-19 Tags: clojure Image: assets/test-preview.png Image-Alt: FIXME Discuss: FIXME Preview: true Write a blog post here! ``` Instead of the boring quickblog default: ``` markdown Title: Test Date: 2024-01-19 Tags: clojure Write a blog post here! ``` If I could but say something like this: ``` text bb quickblog new --file "test.md" --title "Test" --preview --template-file new-post.md ``` assuming I have a `new-post.md` template that looks like this: ``` markdown Title: {{title}} Date: {{date}} Tags: {{tags|join:\",\"}} Image: {% if image %}{{image}}{% else %}{{assets-dir}}/{{file|replace:.md:}}-preview.png{% endif %} Image-Alt: {{image-alt|default:FIXME}} Discuss: {{discuss|default:FIXME}} {% if preview %}Preview: true\n{% endif %} Write a blog post here! ``` I would truly be the happiest of men!