This pull request makes boolean handled like dates and ipv4 addresses: things
are stored as as numerics under the hood and aggregations add some special
formatting logic in order to return true/false in addition to 1/0.
For example, here is an output of a terms aggregation on a boolean field:
```
"aggregations": {
"top_f": {
"doc_count_error_upper_bound": 0,
"buckets": [
{
"key": 0,
"key_as_string": "false",
"doc_count": 2
},
{
"key": 1,
"key_as_string": "true",
"doc_count": 1
}
]
}
}
```
Sorted numeric doc values are used under the hood.
Close#4678Close#7851
08f93cf33f