How to ignore fieldNorm for some fields

[horsley]

For example. two document

doc 1 : {name: "XXX", alias: ["a", "b", "c"]}
doc 2 : {name: "YYY", alias: ["a", "d"]}

In my business I hope that I search alias and the score was equal for this two doc. They have the same TF and IDF, but fieldNorm was different since the fieldLength(terms count) was different. In my case, the terms in this field were synonyms. The number of terms in this field should be ignore when calculate score, so I can sort the result by score, then the name field. If I sort by name field first, the order result became irrelevant totally, that's bad.

[horsley]

fieldNorm was caculated in upsidedown.go. Maybe we can add a field option, configurable via field mapping, for fieldNorm behavior control