allow Zig Zag chain sources

[DaveSkender]

Allow Zig Zag to accept chain sources, to enable smoothing to prevent unusually spikey reversals. It’s okay if endType is limited to single price, without High/Low option. Found in #694

// use chaining to pre-smooth
var results = quotes
    .GetAlma(..)
    .GetZigZag(..);

// use price transforms
var results = quotes
    .Use(..)
    .GetZigZag(..);