Main changes:
* consistency of func arguments, while every argument has both an outer and an inner name,
but the first argument's outer was "unnamed" by default in swift<2. now all arguments are consistent
and requires the initial "_" to declare the outer "unnamed" for the first argument
* indexes are now simpler types, the Array.index function computes successor/predecessor
* many, many API changes, that result in shorter "verb" names of functions with named arguments
ex: Array.joinWithSeparator(String) -> Array.joined(separator: String)
