Session termination by router causes destructor to emit errors/exceptions

[turkanis]

I have found that when the WAMP client's session is terminated unexpectedly by the WAMP router, which can be expected to happen occasionally, the WebSocket client's destructor is called, which in turn calls fwrite(), which triggers a PHP notice with one of several error messages, e.g., "broken pipe". This event can occur outside of any call to the WAMP or WebSocket client, e.g., during unrelated database access.

The pull request #1 addresses the issue by translating errors emitted by fread() and fwrite() into ConnectionExceptions, and by enclosing the code in the destructor in a try/catch block. I have created a similar pull request jszczypk/WampSyncClient#1 for WampSyncClient.