make a hex String from a UInt8 collection

collectionUInt8Extension.swift

// Array of [UInt8] to hex String extension
// let arr = [0x03, 0x00, 0x02, 0x05, 0x11, 0x25, 0xa0, 0xfe, 0xe5] as [UInt8]
// let hex = arr.hexValueString (hex is the result)

extension Collection where Element == UInt8 {
    var hexValueString: String {
        return map{ String(format: "0x%02x", $0) }.joined(separator: ", ")
    }
}