Added error handling code to requests

- Fixed two more cases of 'using';
- Added 'RequestFailure' event to vProto.Request and appropriate
functions;
- Renamed fluent functions for addition of request event handlers -
removed the word 'Request' from the name;
- Added exception argument to internal package type-specific failure
handling functions;
- Heartbeat failure detection no longer accounts received heartbeats -
that was a judgment error;
- Timed out requests are no longer set as aborted too - another judgment
error;
- Changed request status checks in pipe event handlers from !Responded
to Pending - will account for more cases, such as exceptions;
- Added handler for response receipt failure, but won't run for now
because it requires a request ID, which cannot be retrieved in any
current receipt failure case - may be somehow taken care of later;