Merge pull request 'add set float64 func' (#6) from add-set-float64 into master

Reviewed-on: #6

set.go

@@ -1,8 +1,10 @@
 package postgresql
 
 import (
-	"github.com/volatiletech/null/v8"
 	"time"
+
+	"github.com/shopspring/decimal"
+	"github.com/volatiletech/null/v8"
 )
 
 func SetString(val string) null.String {
@@ -45,3 +47,7 @@ func SetJSON(val []byte) (res null.JSON) {
 		Valid: true,
 	}
 }
+
+func SetFloat64(val float64) decimal.Decimal {
+	return decimal.NewFromFloat(val)
+}