This increases composability and avoids some ugly case handling. We
re-export runExceptT in Hledger.Read.
The final return types of the following functions has been changed from
IO (Either String a) to ExceptT String IO a. If this causes a problem,
you can get the old behaviour by calling runExceptT on the output:
readJournal, readJournalFiles, readJournalFile
Or, you can use the easy functions readJournal', readJournalFiles', and
readJournalFile', which assume default options and return in the IO
monad.
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