v0.1.3

Square roots, and a rounding strategy on the operations that round.

Added

• Dec::sqrt, Dec::checked_sqrt and Dec::sqrt_approx. sqrt rounds half
  away from zero at Dec::SCALE and is the one operation here that cannot
  overflow: the largest root the range holds is about 1.3e10, so a negative
  value and NaN are its only failures, which is what checked_sqrt reports as
  None. sqrt_approx goes through f64 for about three times the speed,
  accurate to the double's sixteen significant digits rather than to the last
  place; take it where a root feeds a comparison, not where two of them are
  tested equal.
• RoundingStrategy, taken by Dec::round_dp_with and
  Dec::round_to_step_with: MidpointAwayFromZero, MidpointNearestEven,
  ToZero, AwayFromZero, ToNegativeInfinity and ToPositiveInfinity. Pass
  one where the direction is the exchange's rather than yours: ToZero for a
  quantity filter, the infinity pair for a bid or ask pinned to a tick,
  MidpointNearestEven where many rounded values are summed. It derives
  Default as MidpointAwayFromZero and serialises under the serde feature,
  so a per-instrument policy stores and restores with the instrument.

Changed

• round_dp and round_to_step are unchanged, and are now defined as the
  MidpointAwayFromZero case of their _with counterparts. floor, ceil
  and trunc are the dp 0 cases of the three directed strategies, and say so
  in their docs.
• The arithmetic benchmark is now dec and carries the roots alongside the
  arithmetic, so cargo bench --bench arithmetic is cargo bench --bench dec.
  make bench is unchanged. docs/bench-data.json is re-measured, and the
  site's front page hands off to a Dec page for the per-operation numbers.
• The readme says who writes this crate: every line generated by an AI agent
  under the review of high frequency trading practitioners, and what a
  contribution has to clear before it lands.