Async task returns Result type now.

At this time some strange behaviour is observed:
- ResultFragment has one instance is NetCat (asynctask wrapper);
- this NetCat instance fires off asynctasks on every execute() method call;
- it works great when executing CONNECT and RECEIVE operations;
- RECEIVE op is blocking, but is should only block corresponding asynctask thread;
- but in my case it blocks whole NetCat instance, so new operations doesn't pass to execute() method;
- they only start executing after other side is terminated, connection is closed and RECEIVE op is completed.
Turn out that AsyncTask uses serial executor by default, so READ operation blocks the others.
The use of parallel executor solve the problem.