Adds support for meta lines that only the flymake linter will see.
These are lines prefixed by any number of semicolons followed by a hash
then space. E.g.
;# include "../config.beancount"
;# 2025-01-01 pad Assets:Bank Equity:Opening-Balances
This is useful for silencing the linter in multi-file beancount projects
rather than suffer the usual deluge of multiple-include errors and
redundancies.