add missing datawriter to main.ts

package.json

 {
   "name": "rjsvm",
-  "version": "0.2.1",
+  "version": "0.2.2",
   "description": "",
   "main": "lib/src/main.js",
   "scripts": {

src/main.ts

 export * from "./RJSVM/framework/rjsvm"
+export * from "./RJSVM/datawriter/datawriter"
 export * from "./RJSVM/framework/types"
 export * from "./util/dataparser"