Updating letterboxd-to-markdown to ESM

Updated my letterboxd-to-markdown CLI script last week to use ESM, mostly so I could open a pull request of my fork of letterboxd to add a markdown review method.

The syntax has changed a bit, the main command is now letterboxd diary [account name] (previously letterboxd diary -a [account name]).

The slow move from CommonJS to ESM is confusing, to say the least. Modules that have been updated to support ESM often have documentation that is CommonJS-centric, and most of the blog posts out there are the same. So…lots of trawling through Github issue queues to find workarounds.