Release v1.0.0.

This is the first stable release of jrpc2.

Changes since v0.46.0:

- Update module dependencies.
- Update the versioning statement.
- Update doc comments throughout the module. (#98)
- Update the playground example.

Development of v1 will continue on the main branch of the repository.  If a
major revision becomes necessary, new branches will be added to track a
versioned import path.

README.md

@@ -3,7 +3,7 @@
 [![GoDoc](https://img.shields.io/static/v1?label=godoc&message=reference&color=yellow)](https://pkg.go.dev/github.com/creachadair/jrpc2)
 
 This repository provides a Go module that implements a [JSON-RPC 2.0][spec] client and server.
-There is also a working [example in the Go playground](https://go.dev/play/p/Tr5rdfT-PXi).
+There is also a working [example in the Go playground](https://go.dev/play/p/Nhg0smrxsoM).
 
 ## Packages