1. List the extensions I use explicitly.
2. Use the `iminsert` part instead of `keymap` as it shows the short
code from `b:keymap_name`.
3. Move the file size display part into its own "extension".
4. Update the file size part on-the-fly by using `wordcount()` not more
frequently than 2 seconds.
5. Abuse the extension system for tweaking `maxlinenr` and `colnr`, and
also read their real definitions.
Pretty cool, am I right?
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