UniquePtr: Support SrsUniquePtr to replace SrsAutoFree. v6.0.136 (#4109)

To manage an object:

```cpp
// Before
MyClass* ptr = new MyClass();
SrsAutoFree(MyClass, ptr);
ptr->do_something();

// Now
SrsUniquePtr<MyClass> ptr(new MyClass());
ptr->do_something();
```

To manage an array of objects:

```cpp
// Before
char* ptr = new char[10];
SrsAutoFreeA(char, ptr);
ptr[0] = 0xf;

// Now
SrsUniquePtr<char[]> ptr(new char[10]);
ptr[0] = 0xf;
```

In fact, SrsUniquePtr is a limited subset of SrsAutoFree, mainly
managing pointers and arrays. SrsUniquePtr is better than SrsAutoFree
because it has the same API to standard unique ptr.

```cpp
SrsUniquePtr<MyClass> ptr(new MyClass());
ptr->do_something();
MyClass* p = ptr.get();
```

SrsAutoFree actually uses a pointer to a pointer, so it can be set to
NULL, allowing the pointer's value to be changed later (this usage is
different from SrsUniquePtr).

```cpp
// OK to free ptr correctly.
MyClass* ptr;
SrsAutoFree(MyClass, ptr);
ptr = new MyClass();

// Crash because ptr is an invalid pointer.
MyClass* ptr;
SrsUniquePtr<MyClass> ptr(ptr);
ptr = new MyClass();
```

Additionally, SrsAutoFreeH can use specific release functions, which
SrsUniquePtr does not support.

---------

Co-authored-by: Jacob Su <suzp1984@gmail.com>

trunk/src/app/srs_app_caster_flv.cpp

@@ -215,10 +215,7 @@ srs_error_t SrsDynamicHttpConn::proxy(ISrsHttpResponseWriter* w, ISrsHttpMessage
     
     output = o;
     srs_trace("flv: proxy %s:%d %s to %s", ip.c_str(), port, r->uri().c_str(), output.c_str());
-    
-    char* buffer = new char[SRS_HTTP_FLV_STREAM_BUFFER];
-    SrsAutoFreeA(char, buffer);
-    
+
     ISrsHttpResponseReader* rr = r->body_reader();
     SrsHttpFileReader reader(rr);
     SrsFlvDecoder dec;