makes filter-keys-by-val 9% faster by using into, similar to other fns in ns
makes filter-keys-by-val 9% faster by using into, similar to other fns in ns

(require 'criterium.core)
(require 'useful.map)
(def my-map (zipmap (range 100) (range 100)))

(criterium.core/bench (useful.map/original-filter-keys-by-val odd? my-map))
Evaluation count : 3415500 in 60 samples of 56925 calls.
             Execution time mean : 17.583266 us
    Execution time std-deviation : 124.371912 ns
   Execution time lower quantile : 17.425613 us ( 2.5%)
   Execution time upper quantile : 17.898538 us (97.5%)

Found 2 outliers in 60 samples (3.3333 %)
  low-severe   2 (3.3333 %)
 Variance from outliers : 1.6389 % Variance is slightly inflated by outliers

(criterium.core/bench (useful.map/filter-keys-by-val-with-into odd? my-map))
Evaluation count : 3778800 in 60 samples of 62980 calls.
             Execution time mean : 16.009860 us
    Execution time std-deviation : 89.880836 ns
   Execution time lower quantile : 15.875754 us ( 2.5%)
   Execution time upper quantile : 16.219088 us (97.5%)

Found 2 outliers in 60 samples (3.3333 %)
  low-severe   2 (3.3333 %)
 Variance from outliers : 1.6389 % Variance is slightly inflated by outliers

amalloy/useful,flatland/useful,jafingerhut/useful