remove books.xml and update docs example

Author: zhengchun

books.xml

@@ -0,0 +1,64 @@
+package xmlquery_test
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/antchfx/xmlquery"
+	"github.com/antchfx/xpath"
+)
+
+func Example() {
+	// XPATH syntax and functions see https://github.com/antchfx/xpath
+	s := `<?xml version="1.0"?>
+	<bookstore>
+	   <book id="bk101">
+		  <author>Gambardella, Matthew</author>
+		  <title>XML Developer's Guide</title>
+		  <genre>Computer</genre>
+		  <price>44.95</price>
+		  <publish_date>2000-10-01</publish_date>
+	   </book>
+	   <book id="bk102">
+		  <author>Ralls, Kim</author>
+		  <title>Midnight Rain</title>
+		  <genre>Fantasy</genre>
+		  <price>5.95</price>
+		  <publish_date>2000-12-16</publish_date>
+	   </book>
+	   <book id="bk103">
+		  <author>Corets, Eva</author>
+		  <title>Maeve Ascendant</title>
+		  <genre>Fantasy</genre>
+		  <price>5.95</price>
+		  <publish_date>2000-11-17</publish_date>
+	   </book>
+	</bookstore>`
+
+	doc, err := xmlquery.Parse(strings.NewReader(s))
+	if err != nil {
+		panic(err)
+	}
+	// Quick query all books.
+	books := xmlquery.Find(doc, `/bookstore/book`)
+	for _, n := range books {
+		fmt.Println(n)
+	}
+
+	// Find all books with price rather than 10.
+	books = xmlquery.Find(doc, `//book[price < 10]`)
+	fmt.Println(len(books))
+
+	// Find books with @id=bk102 or @id=bk101
+	books = xmlquery.Find(doc, `//book[@id = "bk102" or @id = "bk101"]`)
+	fmt.Println(len(books))
+
+	// Find books by author: Corets, Eva
+	book := xmlquery.FindOne(doc, `//book[author = "Corets, Eva"]`)
+	fmt.Println(book.SelectElement("title").InnerText()) // > Output: Maeve Ascendant
+
+	// Calculate the total prices of all books
+	nav := xmlquery.CreateXPathNavigator(doc)
+	prices := xpath.MustCompile(`sum(//book/price)`).Evaluate(nav).(float64)
+	fmt.Println(prices) // > Output: 56.85
+}