Post permalinks

[rlskoeser]

• configure nicer permalink format for blog post
• update existing blog post with aliases for their previous urls
• rename excerpt to summary so the post excerpt/summary will actually be displayed on list views

[render[bot]]

Your Render PR Server URL is https://dh-tech-pr-93.onrender.com.

Follow its progress at https://dashboard.render.com/static/srv-ckttreeb0mos73cq3dr0.