added strict test
added between
Merge remote-tracking branch 'schmidt/master'
updated readme.md
fixed between, added some test cases
fixed error in lookupLE
deleted between, becaue it is 3 times slower than loopupRange

benchmarking between
ran 2048 iterations in 2.040148 ms
collecting 100 samples, 1303 iterations each, in estimated 129.8004 ms
analysing with 100000 resamples
mean: 1.004800 us, lb 1.003799 us, ub 1.006028 us, ci 0.950
std dev: 5.676846 ns, lb 4.810024 ns, ub 6.913163 ns, ci 0.950
found 2 outliers among 100 samples (2.0%)
  2 (2.0%) high mild
variance introduced by outliers: 0.990%
variance is unaffected by outliers

benchmarking lookupRange
ran 8192 iterations in 2.582073 ms
collecting 100 samples, 4118 iterations each, in estimated 129.7971 ms
analysing with 100000 resamples
mean: 319.9088 ns, lb 319.5394 ns, ub 320.3216 ns, ci 0.950
std dev: 1.998597 ns, lb 1.783784 ns, ub 2.248989 ns, ci 0.950
variance introduced by outliers: 0.990%
variance is unaffected by outliers
fixed singleton

siseq did not generate LsVal and LsSeL nodes.
another fix in lookupLE
minor changes in comments
in Data.StringMap.Strict a strict update' added, adjust, adjustWithKey and delete added