Convenience methods to add

[sanmai]

• [x] #106
• [x] #107
• [x] #103
• [ ] last(callable $selector = null, $default = null),
• [ ] first(callable $selector = null, $default = null), pull()
• [x] flip (from array_flip) https://github.com/sanmai/pipeline/pull/100
• [ ] nth(int $step, int $offset = 0)
• [x] #109
• [ ] #128
• [ ] #105
• [ ] combine, keysFrom, valuesFrom
• [ ] #104
• [x] max, min https://github.com/sanmai/pipeline/pull/99
• [ ] uniq($keyfn)
• [x] #136
• [ ] dedup()
• [ ] bloomFilter()