Adds retime

[ValentinKaisermayer]

Closes #439

[ValentinKaisermayer]

It works off of #528

[ValentinKaisermayer]

@iblislin What do you think about the interface? I have chosen singleton types instead of Symbols so that a dispatch system can be implemented.

[iblislin]

What do you think about the interface? I have chosen singleton types instead of Symbols so that a dispatch system can be implemented.

well, I personally prefer the Symbol, and build with literal type dispatching.

e.g.

julia> f(::Val{:abc}) = 42
f (generic function with 1 method)

julia> f(x::Symbol) = f(Val(x))
f (generic function with 2 methods)

julia> f(:abc)
42

but I'm not sure about the performance penalty. Maybe you could give that a try.