Add readme and example

Author: spacewander

README.md

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+[![Travis](https://travis-ci.org/spacewander/go-suffix-tree.svg?branch=master)](https://travis-ci.org/spacewander/go-suffix-tree)
+[![GoReportCard](http://goreportcard.com/badge/spacewander/go-suffix-tree)](http://goreportcard.com/report/spacewander/go-suffix-tree)
+[![codecov.io](https://codecov.io/github/spacewander/go-suffix-tree/coverage.svg?branch=master)](https://codecov.io/github/spacewander/go-suffix-tree?branch=master)
+[![license](https://img.shields.io/badge/License-MIT-yellow.svg)](https://github.com/spacewander/go-suffix-tree/blob/master/LICENSE)
+[![godoc](https://img.shields.io/badge/godoc-reference-blue.svg)](https://godoc.org/github.com/spacewander/go-suffix-tree)
+
+# go-suffix-tree
+
+This "suffix" package implements a [suffix tree](https://en.wikipedia.org/wiki/Suffix_tree).
+
+As a suffix tree, it allows to lookup a key in O(k) operations.
+In some cases(for example, some scenes in our production), this can be faster than a hash table because
+   the hash function is an O(n) operation, with poor cache locality.
+
+Plus suffix tree is more memory-effective than a hash table.
+
+## Example
+
+A simple use case:
+```go
+import (
+    suffix "github.com/spacewander/go-suffix-tree"
+)
+
+var (
+    TubeNameTree *suffix.Tree
+    TubeNames = []string{
+        // ...
+    }
+)
+
+func init() {
+    tree := suffix.NewTree()
+    for _, s := range TubeNames {
+        tree.Insert([]byte(s), &s)
+    }
+    TubeNameTree = tree
+}
+
+func getTubeName(name []byte) *string {
+    res, found := TubeNameTree.Get(name)
+    if found {
+        return res.(*string)
+    }
+    return nil
+}
+```
+
+For more usage, see the [godoc](https://godoc.org/github.com/spacewander/go-suffix-tree).

example_test.go

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+package suffix
+
+import (
+	"fmt"
+)
+
+func ExampleInsert() {
+	tree := NewTree()
+	tree.Insert([]byte("sth"), "sth")
+	oldValue, ok := tree.Insert([]byte("sth"), "else")
+	// Always ok
+	if ok {
+		fmt.Println(oldValue.(string))
+	}
+	value, found := tree.Get([]byte("sth"))
+	if found {
+		fmt.Println(value.(string))
+	}
+	// Output:
+	// sth
+	// else
+}
+
+func ExampleGet() {
+	tree := NewTree()
+	tree.Insert([]byte("sth"), "sth")
+	value, found := tree.Get([]byte("sth"))
+	if found {
+		fmt.Println(value.(string))
+	}
+	// Output: sth
+}
+
+func ExampleLongestSuffix() {
+	tree := NewTree()
+	tree.Insert([]byte("table"), "table")
+	tree.Insert([]byte("able"), "able")
+	tree.Insert([]byte("present"), "present")
+	key, value, found := tree.LongestSuffix([]byte("presentable"))
+	if found {
+		fmt.Println("Matched key:", string(key))
+		fmt.Println(value.(string))
+	}
+	// Output:
+	// Matched key: table
+	// table
+}
+
+func ExampleRemove() {
+	tree := NewTree()
+	tree.Insert([]byte("sth"), "sth")
+	oldValue, found := tree.Remove([]byte("sth"))
+	if found {
+		fmt.Println(oldValue.(string))
+	}
+	_, found = tree.Get([]byte("sth"))
+	if !found {
+		fmt.Println("Already removed")
+	}
+	// Output:
+	// sth
+	// Already removed
+}
+
+func ExampleWalk() {
+	tree := NewTree()
+	tree.Insert([]byte("able"), 1)
+	tree.Insert([]byte("table"), 2)
+	tree.Insert([]byte("presentable"), 3)
+	tree.Walk(func(key []byte, _ interface{}) (stop bool) {
+		fmt.Println(string(key))
+		return false
+	})
+	fmt.Println("Walk and stop in the middle:")
+	tree.Walk(func(key []byte, _ interface{}) (stop bool) {
+		fmt.Println(string(key))
+		return string(key) == "able"
+	})
+	// Output:
+	// able
+	// table
+	// presentable
+	// Walk and stop in the middle:
+	// able
+}
+
+func ExampleWalkSuffix() {
+	tree := NewTree()
+	tree.Insert([]byte("able"), 1)
+	tree.Insert([]byte("table"), 2)
+	tree.Insert([]byte("presentable"), 3)
+	tree.Insert([]byte("present"), 4)
+	tree.WalkSuffix([]byte("table"), func(key []byte, _ interface{}) (stop bool) {
+		fmt.Println(string(key))
+		return false
+	})
+	fmt.Println("Walk and stop in the middle:")
+	tree.WalkSuffix([]byte("table"), func(key []byte, _ interface{}) (stop bool) {
+		fmt.Println(string(key))
+		return string(key) == "table"
+	})
+	// Output:
+	// table
+	// presentable
+	// Walk and stop in the middle:
+	// table
+}