algo: Add package algo which implements various basic algorithms.
go fmt *
algo: 53% faster Contains method for SeqList.

benchmark                      old ns/op    new ns/op    delta
BenchmarkSeqListContains1e2          452          212  -53.10%
BenchmarkSeqListContains1e3         4390         1961  -55.33%
BenchmarkSeqListContains1e4        43934        19157  -56.40%
BenchmarkSeqListContains1e5       438878       193781  -55.85%
BenchmarkSeqListContains1e6      4534993      2265760  -50.04%
algo: Simplify the Contains method for SeqList.
algo: Add insertion sort algorithm.