Add godocs for interceptors

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

client.go

@@ -36,6 +36,7 @@ import (
 // closed.
 var ErrClosed = errors.New("ttrpc: closed")
 
+// Client for a ttrpc server
 type Client struct {
 	codec   codec
 	conn    net.Conn
@@ -50,14 +51,17 @@ type Client struct {
 	interceptor UnaryClientInterceptor
 }
 
+// ClientOpts configures a client
 type ClientOpts func(c *Client)
 
+// WithOnClose sets the close func whenever the client's Close() method is called
 func WithOnClose(onClose func()) ClientOpts {
 	return func(c *Client) {
 		c.closeFunc = onClose
 	}
 }
 
+// WithUnaryClientInterceptor sets the provided client interceptor
 func WithUnaryClientInterceptor(i UnaryClientInterceptor) ClientOpts {
 	return func(c *Client) {
 		c.interceptor = i

config.go

@@ -23,6 +23,7 @@ type serverConfig struct {
 	interceptor UnaryServerInterceptor
 }
 
+// ServerOpt for configuring a ttrpc server
 type ServerOpt func(*serverConfig) error
 
 // WithServerHandshaker can be passed to NewServer to ensure that the
@@ -39,6 +40,7 @@ func WithServerHandshaker(handshaker Handshaker) ServerOpt {
 	}
 }
 
+// WithUnaryServerInterceptor sets the provided interceptor on the server
 func WithUnaryServerInterceptor(i UnaryServerInterceptor) ServerOpt {
 	return func(c *serverConfig) error {
 		if c.interceptor != nil {

interceptor.go

@@ -18,20 +18,27 @@ package ttrpc
 
 import "context"
 
+// UnaryServerInfo provides information about the server request
 type UnaryServerInfo struct {
 	FullMethod string
 }
 
+// UnaryClientInfo provides information about the client request
 type UnaryClientInfo struct {
 	FullMethod string
 }
 
+// Unmarshaler contains the server request data and allows it to be unmarshaled
+// into a concrete type
 type Unmarshaler func(interface{}) error
 
+// Invoker invokes the client's request and response from the ttrpc server
 type Invoker func(context.Context, *Request, *Response) error
 
+// UnaryServerInterceptor specifies the interceptor function for server request/response
 type UnaryServerInterceptor func(context.Context, Unmarshaler, *UnaryServerInfo, Method) (interface{}, error)
 
+// UnaryClientInterceptor specifies the interceptor function for client request/response
 type UnaryClientInterceptor func(context.Context, *Request, *Response, *UnaryClientInfo, Invoker) error
 
 func defaultServerInterceptor(ctx context.Context, unmarshal Unmarshaler, info *UnaryServerInfo, method Method) (interface{}, error) {