Appends a number of bytes in-place.
void append (
scope @safe size_t delegate(scope AllocAppender
. ElemType dst) del
The delegate will get the memory slice of the memory that follows
the already written data. Use
reserve to ensure that this slice
has enough room. The delegate should overwrite as much of the
slice as desired and then has to return the number of elements
that should be appended (counting from the start of the slice).