Incorrect function used in the avio_reading.c example

[Ferneu]

The avio_reading.c example uses av_freep() to free the AVIOContext it allocated with avio_alloc_context()

I believe it should be using avio_context_free() instead.

And while we are at it, you guys should really consider completely removing the buffer avio_alloc_context() requires/allow the user to pass. Since according to the docs the AVIOContext is free to reallocate that buffer at will and, in my experience, it usually does that, the user always ends up with a dangling pointer in case he was hoping to perform some sane resource management (i.e., free the things he allocated).

The "correct" way to free the AVIOContext (first call av_freep(&avio_ctx->buffer) and then free the context itself) is not intuitive at all, and since you guys already have avio_context_free(), you should make it take care of doing that.

[Jun Zhao]

Refer to the commit a0877648472a25debc9bd7957684748a253c2b52, Thanks.

BTW: Update API as the suggestion is the other issue, I think.