Release prep for 0.19.0

[jsdw]

#471 in-particular has come up a few times now, so the main impetus for this release is getting that out there, so that event subscriptions are able to be carried out in things like tokio tasks without hitting Send related issues.

Changes:

• Return events from blocks skipped over during Finalization, too (Return events from blocks skipped over during Finalization, too #473)
• Use RPC call to get account nonce (Use RPC call to get account nonce #476)
• Add script to generate release changelog based on commits (Generate release changelog based on commits #465)
• README updates (Update README #472)
• Make EventSubscription and FilterEvents Send-able (Make EventSubscription and FilterEvents Send-able #471)

[lexnv]

This seems like a mismatch generated by ./scripts/generate_changelog.sh.

It seems that the script inspects git config --get remote.origin.url, which is not always expected to be a browser URL. Will do a quick fix for it in the meanwhile.

[jsdw]

oooh indeed; I didn't pay attention to those URLs :)