add doc for heap (#76)

README.md

@@ -180,7 +180,7 @@ See C++ STL.
 
 #### heap
 
-Heap provides basic min heap algorithms:
+[Heap](heap.md) provides basic min heap algorithms:
 
 - `MakeMinHeap` Convert a slice to a min heap
 - `IsMinHeap` Check whether a slice is a min heap
@@ -198,6 +198,8 @@ and variants with custome comparasion function:
 
 both of them are mush faster and easier to use than [container/heap](https://pkg.go.dev/container/heap).
 
+See detailed usage and benchmark report in the [document of heap](heap.md)。
+
 ### Interface Design and Naming
 
 The design leart much from the C++ STL. The `T` here represents `template`. Yes, Go's generic is not template. but who made C++ so influential and STL so famous?

README_zh.md

@@ -182,6 +182,8 @@ func TestSkipList_ForEachMutable(t *testing.T) {
 
 都比 go 标准库 [container/heap](https://pkg.go.dev/container/heap) 更容易使用且更快。
 
+用法和测试详情参见[heap的文档](heap.md)。
+
 ### 接口设计和命名
 
 较多地参考了 C++ STL。T 表示模板。是的，Go 的范型不是模板，但是谁让 C++ 那么影响力，而 STL 又那么有名呢。

heap.md

@@ -0,0 +1,84 @@
+# Heap
+
+## Easy to use
+
+For ordered types, you can easily use the heap algorithms, for example, with `int` type:
+
+```go
+func Example() {
+    heap := []int {5, 4, 3, 2, 1}
+    stlgo.MakeHeap(heap)
+    stl4go.PushMinHeap(&heap, 6)
+    stl4go.PopMinHeap(&heap)
+}
+```
+
+Please compare with [container/heap](https://pkg.go.dev/container/heap#example-package-IntHeap):
+
+```go
+// This example demonstrates an integer heap built using the heap interface.
+package main
+
+import (
+	"container/heap"
+	"fmt"
+)
+
+// An IntHeap is a min-heap of ints.
+type IntHeap []int
+
+func (h IntHeap) Len() int           { return len(h) }
+func (h IntHeap) Less(i, j int) bool { return h[i] < h[j] }
+func (h IntHeap) Swap(i, j int)      { h[i], h[j] = h[j], h[i] }
+
+func (h *IntHeap) Push(x any) {
+	// Push and Pop use pointer receivers because they modify the slice's length,
+	// not just its contents.
+	*h = append(*h, x.(int))
+}
+
+func (h *IntHeap) Pop() any {
+	old := *h
+	n := len(old)
+	x := old[n-1]
+	*h = old[0 : n-1]
+	return x
+}
+
+// This example inserts several ints into an IntHeap, checks the minimum,
+// and removes them in order of priority.
+func main() {
+	h := &IntHeap{2, 1, 5}
+	heap.Init(h)
+	heap.Push(h, 3)
+	fmt.Printf("minimum: %d\n", (*h)[0])
+	for h.Len() > 0 {
+		fmt.Printf("%d ", heap.Pop(h))
+	}
+}
+```
+
+You must define a new type `IntHeap` and five methods before to use the library,
+these boilerplate codes are verbose, tedious, and boring.
+
+## Benchmark
+
+The heap algorithms are also much faster than `container/heap`, even for the `Func` version.:
+
+```console
+% go test -bench BenchmarkHeap
+goos: darwin
+goarch: arm64
+pkg: github.com/chen3feng/stl4go
+BenchmarkHeapInit/container/heap.Init-10                  362450              3172 ns/op
+BenchmarkHeapInit/stlgo.MakeMinHeap-10                    960280              1136 ns/op
+BenchmarkHeapInit/stlgo.MakeHeapFunc-10                   483109              2336 ns/op
+BenchmarkHeapPush/container/heap.Push-10                  101822             11639 ns/op
+BenchmarkHeapPush/stlgo.PushMinHeap-10                    501031              2283 ns/op
+BenchmarkHeapPush/stlgo.PushHeapFunc-10                   437288              2634 ns/op
+BenchmarkHeapPop/container/heap.Pop-10                     14550             82170 ns/op
+BenchmarkHeapPop/stlgo.PopMinHeap-10                       62139             19782 ns/op
+BenchmarkHeapPop/stlgo.PopHeapFunc-10                      22693             52900 ns/op
+PASS
+ok      github.com/chen3feng/stl4go     17.670s
+```