make gnoblog-cli extract the title from markdown and remove title: from frontmatter.

[moul]

Instead of setting the title as frontmatter metadata and manually removing the first markdown title (#), we should do the opposite. This will make things clearer, easier to review, and result in a better rendering of the source file on GitHub.

We can accomplish this in a single PR by updating gnoblog-cli to extract the title from the markdown and by updating existing blog posts to adhere to the new expected behavior.

[leohhhn]

Will be fixed in #63.

[leohhhn]

Closed by #63.