constantinople support (JSVM)

run remix-lib tests on v0.5.4+commit.9549d8ff

fix: handle bignumber conversion on hash without prefix

ethereum/populus is no longer maintained. Use ours.

Updated regex in Memory Debugger to exclude replacing space with '?'

Fix test

fix: storageRangeAt doesn't always take a callback

Allow timestamps to be passed to rawRun

This is useful when, for example, running a recorded .json
file for cases that rely on a specific time between transactions.

If no timestamp is passed as part of the tx argument to
runRaw, behavior does not change.

Add module declaration

Update README.md