Clean up the listen thread when it's finished.
Pass connection errors on to the callee through the close_handler.
Merge branch 'pull_exception_handling' into dev

Conflicts:
	lib/tubesock.rb
Fix NPE on unclean browser exits.
Merge branch 'pull_keepalive_thread_npe' into dev
Add server side timeout management with websocket ping/pong-mechanism.
Add support for close with cause.
Pass connection errors on to the callee through the close_handler.
Merge branch 'pull_exception_handling' into dev

Conflicts:
	lib/tubesock.rb
Merge branch 'pull_keepalive_thread_npe' into dev
Merge branch 'pull_ping_pong_management' into dev

Conflicts:
	README.md
	lib/tubesock.rb