Rematch should probably use `isequal` instead of `==` for floating-point types

This:
```julia
using Rematch
nan = 0.0 / 0.0
f(x) = @match x begin
    [a,a] => :same
    [a,b] => :different
    _ => :other
end
println(f([nan, nan]))
```
prints "different".
