Added support for the 'expand:renderfields' option

A couple of fields can be rendered server side, especially the ones
related to dates (that can become string like "2 hours ago"), and the
comments body that can be expanded from JIRA wiki markup into HTML.
A new type IssueRenderedFields has been introduced with a couple of
fields that can be expanded.

examples/renderedfields/main.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"net/http"
+	"os"
+	"strings"
+	"syscall"
+
+	jira "github.com/andygrunwald/go-jira"
+	"golang.org/x/crypto/ssh/terminal"
+)
+
+func main() {
+	r := bufio.NewReader(os.Stdin)
+
+	fmt.Print("Jira URL: ")
+	jiraURL, _ := r.ReadString('\n')
+
+	fmt.Print("Jira Issue key: ")
+	key, _ := r.ReadString('\n')
+	key = strings.TrimSpace(key)
+
+	fmt.Print("Jira Username: ")
+	username, _ := r.ReadString('\n')
+
+	fmt.Print("Jira Password: ")
+	bytePassword, _ := terminal.ReadPassword(int(syscall.Stdin))
+	password := string(bytePassword)
+
+	var tp *http.Client
+
+	if strings.TrimSpace(username) == "" {
+		tp = nil
+	} else {
+
+		ba := jira.BasicAuthTransport{
+			Username: strings.TrimSpace(username),
+			Password: strings.TrimSpace(password),
+		}
+		tp = ba.Client()
+	}
+
+	client, err := jira.NewClient(tp, strings.TrimSpace(jiraURL))
+	if err != nil {
+		fmt.Printf("\nerror: %v\n", err)
+		return
+	}
+
+	fmt.Printf("Targetting %s for issue %s\n", strings.TrimSpace(jiraURL), key)
+
+	options := &jira.GetQueryOptions{Expand: "renderedFields"}
+	u, _, err := client.Issue.Get(key, options)
+
+	if err != nil {
+		fmt.Printf("\n==> error: %v\n", err)
+		return
+	}
+
+	fmt.Printf("RenderedFields: %+v\n", *u.RenderedFields)
+
+	for _, c := range u.RenderedFields.Comments.Comments {
+		fmt.Printf("  %+v\n", c)
+	}
+}