tries to copy the given buffer to the end of the last chained buffer. If there's not enough room it returns false

clear one (frees) */

availability is a string where each character is the availability of that piece, '1', '2' etc. have_str is a string where each character represents a

will update the piece with the given properties (priority, elem_index) to place it at the correct position

returns one of the valid download categories of state_t or piece_open if this piece is not being downloaded