func (q *Query) FilterQuery(fq string) {
	q.params.Add("fq", fq)
}
fq (Filter Query) http://wiki.apache.org/solr/CommonQueryParameters
Example: popularity:[10 TO *]
package solr
import (
	"fmt"
	"net/url"
)
type Query struct {
	params *url.Values
}
func NewQuery() *Query {
	q := new(Query)
	q.params = &url.Values{}
	return q
}
func (q *Query) AddParam(k, v string) {
	q.params.Add(k, v)
}
func (q *Query) RemoveParam(k string) {
	q.params.Del(k)
}
func (q *Query) GetParam(k string) string {
	return q.params.Get(k)
}
func (q *Query) SetParam(k, v string) {
	q.params.Set(k, v)
}
func (qq *Query) Q(q string) {
	qq.params.Add("q", q)
}
func (q *Query) Sort(sort string) {
	q.params.Add("sort", sort)
}