Release v5.9

At long last support for traversing through slice, array and maps and validating at any or all levels!

see documentation for the new "dive" tag

benchmarks have slightly increased ns/op and B/ops for this functionality and an additional allocation for single field validation.

$ go test -cpu=4 -bench=. -benchmem=true
PASS
BenchmarkValidateField-4             3000000           439 ns/op         192 B/op          2 allocs/op
BenchmarkValidateStructSimple-4      1000000          2382 ns/op         656 B/op         10 allocs/op
BenchmarkTemplateParallelSimple-4    2000000           910 ns/op         656 B/op         10 allocs/op
BenchmarkValidateStructLarge-4        100000         13201 ns/op        4309 B/op         60 allocs/op
BenchmarkTemplateParallelLarge-4      300000          5240 ns/op        4311 B/op         60 allocs/op

for #78