ledger v2.0.11

• register_beancount() and register_hledger() now import a transaction id column (#21).
  Thanks @vikasrawal for suggestion.
• register_beancount() now coerces the date column to a "Date" object.
  register_ledger() and register_hledger() already did so.
• register_ledger() now trims the comment column with stringr::str_trim().