Struct related to interval faceting query.

Example

iex> x = %Hui.Query.FacetInterval{interval: "price", set: ["[0,10]", "(10,100]"]}
%Hui.Query.FacetInterval{
  interval: "price",
  set: ["[0,10]", "(10,100]"],
  per_field: false
}
iex> y = %Hui.Query.Facet{interval: x, field: ["type", "year"]}
%Hui.Query.Facet{
  contains: nil,
  "contains.ignoreCase": nil,
  "enum.cache.minDf": nil,
  excludeTerms: nil,
  exists: nil,
  facet: true,
  field: ["type", "year"],
  interval: %Hui.Query.FacetInterval{
    interval: "price",
    set: ["[0,10]", "(10,100]"],
    per_field: false
  },
  limit: nil,
  matches: nil,
  method: nil,
  mincount: nil,
  missing: nil,
  offset: nil,
  "overrequest.count": nil,
  "overrequest.ratio": nil,
  pivot: nil,
  "pivot.mincount": nil,
  prefix: nil,
  query: nil,
  range: nil,
  sort: nil,
  threads: nil
}
iex> y |> Hui.Encoder.encode # render struct into URL query string with `facet` prefixes
"facet=true&facet.field=type&facet.field=year&facet.interval=price&facet.interval.set=%5B0%2C10%5D&facet.interval.set=%2810%2C100%5D"

Example - per field intervals, f.[fieldname].facet.interval

iex> x = %Hui.Query.FacetInterval{interval: "price", set: ["[0,10]", "(10,100]"], per_field: true}
%Hui.Query.FacetInterval{
  interval: "price",
  set: ["[0,10]", "(10,100]"],
  per_field: true
}
iex> y = %Hui.Query.Facet{field: "type", interval: x}
%Hui.Query.Facet{
  contains: nil,
  "contains.ignoreCase": nil,
  "enum.cache.minDf": nil,
  excludeTerms: nil,
  exists: nil,
  facet: true,
  field: "type",
  interval: %Hui.Query.FacetInterval{
    interval: "price",
    set: ["[0,10]", "(10,100]"],
    per_field: true
  },
  limit: nil,
  matches: nil,
  method: nil,
  mincount: nil,
  missing: nil,
  offset: nil,
  "overrequest.count": nil,
  "overrequest.ratio": nil,
  pivot: nil,
  "pivot.mincount": nil,
  prefix: nil,
  query: nil,
  range: nil,
  sort: nil,
  threads: nil
}
iex> y |> Hui.Encoder.encode
"facet=true&facet.field=type&facet.interval=price&f.price.facet.interval.set=%5B0%2C10%5D&f.price.facet.interval.set=%2810%2C100%5D"