fix buffer read/write

[salix5]

https://gist.github.com/shafik/848ae25ee209f698763cffee272a58f8
According to the strict aliasing rule, we should not cast a pointer should to another type and dereference.
It can be done by memcpy.

C++14
3.10, paragraph 10

If a program attempts to access the stored value of an object through a glvalue of other than one of the
following types the behavior is undefined:
—(10.1) the dynamic type of the object,
—(10.2) a cv-qualified version of the dynamic type of the object,
—(10.3) a type similar (as defined in 4.4) to the dynamic type of the object,
—(10.4) a type that is the signed or unsigned type corresponding to the dynamic type of the object,
—(10.5) a type that is the signed or unsigned type corresponding to a cv-qualified version of the dynamic type
of the object,
—(10.6) an aggregate or union type that includes one of the aforementioned types among its elements or non-
static data members (including, recursively, an element or non-static data member of a subaggregate
or contained union),
—(10.7) a type that is a (possibly cv-qualified) base class type of the dynamic type of the object,
—(10.8) a char or unsigned char type.

Add buffer.h

Reference:
https://github.com/edo9300/edopro/blame/master/gframe/bufferio.h

[salix5]

@mercury233
@purerosefallen
Can we merge this one?

[purerosefallen]

I doubt if reconnecting works

[salix5]

I only changed buffer writing to the way it should be.
I don't think it will change reconnecting.