Wrap commit body in code area in PR message

[leoluk]

Stack:

• Use emojis for "spr status" output #155
• Support the "gh" CLI tool in addition to "hub" #156
• Only update run count when user is not already a stargazer #154
• Do not panic on runtime errors #153
• Manual merge notice #152
• README.md: document how to install from source #151
• Wrap commit body in code area in PR message #150 ⮜
• Mark current position in stack #149
• Include https:// in PR link #148
• Reformat PR comment messages #147

Commit messages are not guaranteed to be valid Markdown.
Wrapping them in a code area guarantees that the original
formatting is preserved (say, ASCII art).

This matches what GitHub itself does when rendering commits.

This might be a matter of taste - maybe some people *do*
write valid Markdown in their commits and want to keep the
existing behavior - should we make it a config option?

⚠️ Part of a stack created by spr. Do not merge manually using the UI - doing so may have unexpected results.

[ejoffe]

I have never seen anyone use markdown in commit messages, so I'm good with this.
We can add it as a configuration layer if there is a need for markdown commit message support.

[leoluk]

✓ Commit merged in pull request #156