hledger has represented quantities with floating point (Double) until
now. While this has been working fine in practice, the time has come to
upgrade our number representation to something more principled: Decimal,
for now. As a bonus, this brings a ~30% speed boost to most reports.
We'll keep the old representation(s) around for a while, selectable via
hledger-lib cabal flag, for research/testing/benchmarking purposes. To
build with the old Double representation: cabal install -fdouble
hledger-lib hledger hledger-web