* feat(providers): return a PendingTransaction from send_tx calls
* feat(providers): expose the internal provider to all middlewares
* fix(middleware): use the returned PendingTx instead of using a hash
* fix(contract): use the pending tx returned value
Note1: To support that, we need to clone the tx when sending in order to make lifetimes work out
Note2: Multicall does not support that feature
* fix(ethers): adjust examples
* chore: fix provider test
* chore: fix celo test
BREAKING CHANGE
* fix(signers): make Signer send by blocking on Ledger calls
* fix(providers): use Arc in WS impl to allow cloning
* feat(middleware): add geometric gas price escalator
* test(middleware): ensure that we can still stack everything up
* fix(middleware): default to tokio/async-std
* chore: fix clippy
* docs(middleware): add docs and rename middlewares
* chore: fix doctests
* feat: add linear gas escalator
https://github.com/makerdao/pymaker/blob/master/tests/test_gas.py\#L107https://github.com/makerdao/pymaker/blob/master/pymaker/gas.py\#L129
* feat: add constructors to gas escalators
Georgios Konstantopoulos