* add slate upgrading/downgrading
* add slate versions
* slate versioning compilation and tests
* transaction slate responses downgrade themselves to the version of the caller
* add command line arg for target slate version output
* v2 versioning comment info
* doctest fixes
* APIv2 Rewrite first draft
Add WIP JSON RPC handler for APIOwner via proc-macro generated API, using the easy-jsonrpc crate.
* patch dependency on grin core to get serializable errors
* doctest ownerapi, update easyjsonrpc version
* begin impl ForeignApi
* https://github.com/mimblewimble/grin/pull/2659 is merged, switch from using forked repo
* write jsonrpc doctests for ForeignApi