Support some syntax sugar
1. context.arg('path.to.prop')
2. context.arg('name', defaultValue);
3. context.getRes('path.to.result', defaultValue);
4. context.getRes();
5. context.args()
6. Imporove context.toJSON() (add params property)
Merge pull request #188 from golyshevd/i186

Support some syntax sugar