Method reset

API/fleece/slice.hh:375–375

Releases and clears; same as assigning `nullslice`.

        /// Releases and clears; same as assigning `nullslice`.
        void reset() noexcept                               {release(); assignFrom(nullslice);}
        /// Resets to an uninitialized block of the given size.
        void reset(size_t sz)                               {*this = alloc_slice(sz);}
        /// Changes the size of the block by re-allocating. This changes `buf`!