Move common crates to parity-common

[dvdplm]

To enable more ergonomic use and easier maintenance of crates in parity-ethereum in other projects, move common crates to a new parity-common repo and publish the subcrates to crates.io.

As a first approximation "common crates" are crates used both in parity-ethereum and Polkadot and that are not ethcore.

This work will be on-going and this here ticket is mostly about defining the basic premises and creating infrastructure.

• create parity-common repo –> https://github.com/paritytech/parity-common
• create the list of parity-ethereum crates used in Polkadot
• move over a few easy cases -> https://gist.github.com/dvdplm/018e8d919d30f5df7b850a561a8c1637
• set up CI for parity-common
• make any changes needed to parity-ethereum build&release scripts
• make any changes needed to polkadot build&release scripts
• update/reshuffle docs as needed
• publish the subcrates in parity-common to crates.io

[dvdplm]

cc @5chdn @gavofyork @folsen looks about right to you?

[5chdn]

is ethcore-* only used by parity ethereum?

[dvdplm]

Yes, at least I believe so. I think the sentiment when discussing this was that the ethcore crate is so big and somewhat unstructured that moving it (or any of the parts) would be a big undertaking. We'd risk ending up with all of parity-ethereum in parity-common.

(Note that there's at least one ethcore-* that is not part of the ethcore crate: ethcore-bytes. That one we can and will move.)

[5chdn]

if we move anything from ethcore-* to parity-common, please rename it to parity-*

Because once in common, it's not ethereum specific anymore.