adjust Sine Function1

The sine Function1 currently takes frequency as cycles per second, and thus multiplies by 2 PI. For some times cycles (eg, seasonal variations), this is quite unnatural.

• propose supporting frequency or period, where period is in seconds.
• potentially useful to add an optional phase shift, for cases where a time shift may be less appropriate.
• clip min/max limits. Eg ensures we maintain min levels

@orgogozo