This change adds a new command line tool to the Splash family:
`SplashMarkdown`.
It’s an adapted version of the tool that I’ve been using for months to
publish every article on Swift by Sundell, and works by replacing all
code blocks within a Markdown file.
Adding this will hopefully make Splash even easier to use, without the
need for writing custom tooling, or to manually replace each code block
within a Markdown file with a “splashed” version.
This patch makes `HTMLOutputFormat` correctly escape all < and > characters
that occur in source code. Otherwise, a web browser rendering the resulting
HTML will interpret those characters as tags.
