Moved addition into action.

src/action.rs

@@ -1,4 +1,5 @@
 mod action_type;
+mod addition;
 mod calculation;
 mod message;
 mod query;
@@ -10,6 +11,7 @@ pub use crate::document::{
     field::{Field, FieldType},
 };
 pub use action_type::Action;
+pub use addition::Addition;
 pub use calculation::{CalcValue, Calculation, Operand};
 pub use message::MsgAction;
 pub use query::Query;