docs: Update for rpc/jsonrpc/types/v4 module.

This updates the following to reflect the new module version:

- The rpc/jsonrpc/types/README.md file
- The docs/README.md file
- The module hierarchy graphviz
- The module hierarchy diagram

docs/README.md

@@ -175,7 +175,7 @@ The following versioned modules are provided by dcrd repository:
   a robust and easy to use Websocket-enabled Decred JSON-RPC client
 * [dcrjson/v4](https://github.com/decred/dcrd/tree/master/dcrjson) - Provides
   infrastructure for working with Decred JSON-RPC APIs
-* [rpc/jsonrpc/types/v3](https://github.com/decred/dcrd/tree/master/rpc/jsonrpc/types) -
+* [rpc/jsonrpc/types/v4](https://github.com/decred/dcrd/tree/master/rpc/jsonrpc/types) -
   Provides concrete types via dcrjson for the chain server JSON-RPC commands,
   return values, and notifications
 * [wire](https://github.com/decred/dcrd/tree/master/wire) - Implements the

docs/assets/module_hierarchy.gv

@@ -8,7 +8,7 @@ digraph {
 	bech32 [label="bech32" fillcolor=antiquewhite3]
 	chainhash [label="chaincfg/chainhash" fillcolor=aquamarine]
 	dcrjson [label="dcrjson/v4" fillcolor=indianred]
-	types [label="rpc/jsonrpc/types/v3" fillcolor=tomato]
+	types [label="rpc/jsonrpc/types/v4" fillcolor=tomato]
 	wire [label="wire" fillcolor=coral]
 	addrmgr [label="addrmgr/v2" fillcolor=lightsalmon]
 	chaincfg [label="chaincfg/v3" fillcolor=cadetblue]

rpc/jsonrpc/types/README.md

@@ -3,7 +3,7 @@ jsonrpc/types
 
 [![Build Status](https://github.com/decred/dcrd/workflows/Build%20and%20Test/badge.svg)](https://github.com/decred/dcrd/actions)
 [![ISC License](https://img.shields.io/badge/license-ISC-blue.svg)](http://copyfree.org)
-[![Doc](https://img.shields.io/badge/doc-reference-blue.svg)](https://pkg.go.dev/github.com/decred/dcrd/rpc/jsonrpc/types/v3)
+[![Doc](https://img.shields.io/badge/doc-reference-blue.svg)](https://pkg.go.dev/github.com/decred/dcrd/rpc/jsonrpc/types/v4)
 
 Package types implements concrete types for marshalling to and from the dcrd
 JSON-RPC commands, return values, and notifications.  A comprehensive suite of