lessThan / moreThan Filter

For timeUnit, we can’t just use expression. Using range with null values make spec not very readable.

So I think we better support lessThan / moreThan filter.
And perhaps, lessThanOrEqual / moreThanOrEqual.

[domoritz]

greaterThan not moreThan is the standard name for >. If you want brevity, we can use gt which is standard in many query languages. E.g.: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-range-query.html

[kanitw]

Let’s say gt, gte, lt, lte then.