aws simple is now on hackage

introduce SQS backend and add alive hearbeats to queue backends

remove bad client test as it is flakey

remove one test

add node about backends in cabal file

add a network distributed queue worker

ci: don't build benchmarks for nightly build

ci: next leveldb installation fix

ci: next attempt for correct leveldb version in travis

ci: next attempt at making travis happy

ci: next attempt to fix travis...

ci: the next attempt to make travis happy

make enqueuing nonblocking and report success info

ci: do not unset CC

ci: attempt to solve linking issues