openassets-ruby v0.7.0

This release is for Bitcoin Core 0.18.0 integration.

Openassets::Api relies on Bitcoin Core wallet features.

When signing a transaction that issues or transfers an asset, signrawtransaction rpc was called. But in Bitcoin Core 0.18.0, signrawtransaction rpc was removed.

In version v0.7.0, if the destination Bitcoin Core does not support signrawtransaction rpc, Openassets::Api will call signrawtransactionwithwallet rpc instead.