GitLab

Limits connection bandwidth in real world benchmarks so that blocks are delayed if single peer is
overused

fix #40

make both performance benchmarks write to a tmp dir and put in the .gitignore

- moved sessions out of main bitswap package
- modified session manager to manage all sessions
- moved get functions to their own package so sessions can directly

BREAKING CHANGE: SessionsForBlock, while not used outside of Bitswap, has been removed, and was an
exported function

- add a delay generator that similates real world latencies one might encounter on the internet
- modify virtual network to accept different latencies for different
peers based on using NextWaitTime on passed delay
- modify dup_blocks_test subtestDistributeAndFetch to accept a custom
delay
- Add a real world benchmarks that simulates the kinds of problems one might
encounter bitswaping with a long lived session and a large swarm of
peers with real world latency distributions (that causes #8 not to
function well in practice)

So that CI passes, and because it's not reliable as a test, and is more a benchmark to measure
performance, convert dup_block_test.go to a benchmark, which can be run using `go test -bench .`