feat(options): Intent to ship data.groupsZeroAs

[netil]

Issue

#2813

Details

Implement the way to specify how zero value is treated on groups

Possible values:

• zero: 0 will be positioned at absolute axis zero point.
• positive: 0 will be positioned at the top of a stack.
• negative: 0 will be positioned at the bottom of a stack.

data: {
  columns: [
    ["data1", -11, -11, -11, -11],
    ["data2", 4, 4, 4, 4],
    ["data3", 0, 1, 0, -1]
  ],
  type: "area",
  order: null,
  groups: [
    ["data1", "data2", "data3"]
  ],
  groupsZeroAs: "positive"
}

[coveralls]

Coverage increased (+0.01%) to 90.523% when pulling b81c7dd on netil:groupsZero#2813 into e7bdbbc on naver:master.