CSV reader version 2 with new rules syntax

At long last. The main change is a new rules file format that aims to
be more powerful and more intuitive than v1 (hledger 0.19.x and older).
Existing rules files will need to be adapted manually to the new format.

hledger-lib/Hledger/Data/Types.hs

@@ -180,42 +180,6 @@ data Reader = Reader {
 
 instance Show Reader where show r = "Reader for "++rFormat r
 
--- data format parse/conversion rules
-
--- currently the only parse (conversion) rules are those for the CSV format
-type ParseRules = CsvRules
-
--- XXX copied from Convert.hs
-{- |
-A set of data definitions and account-matching patterns sufficient to
-convert a particular CSV data file into meaningful journal transactions. See above.
--}
-data CsvRules = CsvRules {
-      dateField :: Maybe FieldPosition,
-      dateFormat :: Maybe String,
-      statusField :: Maybe FieldPosition,
-      codeField :: Maybe FieldPosition,
-      descriptionField :: [FormatString],
-      amountField :: Maybe FieldPosition,
-      amountInField :: Maybe FieldPosition,
-      amountOutField :: Maybe FieldPosition,
-      currencyField :: Maybe FieldPosition,
-      baseCurrency :: Maybe String,
-      accountField :: Maybe FieldPosition,
-      account2Field :: Maybe FieldPosition,
-      date2Field :: Maybe FieldPosition,
-      baseAccount :: AccountName,
-      accountRules :: [AccountRule],
-      skipLines :: Int
-} deriving (Show, Eq)
-
-type FieldPosition = Int
-
-type AccountRule = (
-   [(String, Maybe String)] -- list of regex match patterns with optional replacements
-  ,AccountName              -- account name to use for a transaction matching this rule
-  )
-
 -- format strings
 
 data HledgerFormatField =