Alias for input Signals

[JobJob]

Previously you could use e.g. Input(2) to create an "input" signal, now you use Signal(2). Should we add an alias to Signal, e.g. input? It would be more consistent with the other operators that create Signals that all have lower case names (map, filter, etc), and more intuitive, to me at least.

[shashi]

Sounds fine to me! I quite like how the capitalization in Signal denotes the fact that it's a constructor though.