Added delimit function, tests and docs

Added a new function, delimit, that takes a slice, array or map and returns a string with all the values delimited by the specified string.
Couldn’t that be:

```go
func Delimit(seq interface{}, delimiter, last... string) (string, error) {
```

My thought there is that delimiter should always be a string, and it *should* be possible with `last...` to support a “last delimiter” that would fix the “and” problem.