add options to set custom namespace separator and a method name transformer

[raul0ligma]

helps create eth_* friendly rpc methods by allowing custom options
example:

rpcServer := jsonrpc.NewServer(
		jsonrpc.WithNamespaceSeparator("_"),
		jsonrpc.WithMethodNameTransformer(func(s string) string {
			r := []rune(s)
			r[0] = unicode.ToLower(r[0])
			return string(r)
		}),
	)

	rpcServer.Register("eth", ethRpcService)	
        ...
        
        // this would become eth_blockNumber 
        (r *EthRpc) BlockNumber(ctx context.Context) 

[Stebalien]

This seems like a reasonable improvement. Thanks!

[Stebalien]

How about letting the user control everything with a "method name formatter". I.e.:

1. Define a WithMethodNameFormatter option that takes a func(namespace, method string) string.
2. Default to func(namespace, method) string { return namespace + "." + name }.

That way the user can combine the method name and namespace in any way they want.

Also, please don't modify method.Name (it's probably safe, but I would avoid it).

[Stebalien]

E.g., in case the user wants something like method.namepace or /namespace/method etc.

[raul0ligma]

s.methods[s.methodNameFormatter(namespace, method.Name)] = methodHandler{
			paramReceivers: recvs,
			nParams:        ins,

			handlerFunc: method.Func,
			receiver:    val,

			hasCtx:       hasCtx,
			hasRawParams: hasRawParams,

			errOut: errOut,
			valOut: valOut,
		}

add a formatter handler now and defaults to namespace.method

[Stebalien]

Thanks!