Reactivecocoa: Convert free functions to static functions

Should non-instance methods be free functions or static functions?

Because currently we have:

extension SignalType {

    /// Merges the given signals into a single `Signal` that will emit all values
    /// from each of them, and complete when all of them have completed.
    @warn_unused_result(message="Did you forget to call `observe` on the signal?")
    public static func merge<S : SequenceType where S.Generator.Element == Signal<Value, Error>>(signals: S) -> ReactiveCocoa.Signal<Self.Value, Self.Error>
}

But we also have:

/// Combines the values of all the given signals, in the manner described by
/// `combineLatestWith`.
@warn_unused_result(message="Did you forget to call `observe` on the signal?")
public func combineLatest<A, B, Error>(a: Signal<A, Error>, _ b: Signal<B, Error>) -> Signal.Signal<(A, B), Error>

We should standardize on one or the other for RAC 5.0.

I'd vote free functions, but I'm curious if someone thinks we should be using static functions. @ReactiveCocoa/reactivecocoa