Merge branch 'master' into refactor/substrate-state-machine-generic

* master:
  Collator for the "adder" (formerly basic-add) parachain and various small fixes (#438)
  Storage changes subscription (#464)
  Wasm execution optimizations (#466)
  Fix the --key generation (#475)
  Fix typo in service.rs (#472)
  Fix session phase in early-exit (#453)
  Make ping unidirectional (#458)
  Update README.adoc