- replaced int id_dest member of edge with state *target pointer
- added bool accept_reject member to edge
  added edge_new_accept_reject(...) and edge_init_accept_reject(...)
  added error handling in edge.c
- changed all edge_default (in parameters and so on) references to edge!
  because edge will become more powerful because tape_actions will become
  more powerful
- removed enum STATE_TYPE because we solved this better
- removed tape_action.h, tape_action.c and moved this functionality to
  tape_actions completely
- replaced data member of tape_actions with three arrays:
    vec_read - array of uintptr_t pointers (read vector)
    vec_write - array of uintptr_t pointers (write vector)
    vec_dirs - array of SHIFT_DIR enums (direction vector
- removed priv member from tape
- added safety checks in state.c tape_cell_list.c, tape_cell.c,
  tape_actions.c, tm.c, edge_list.c, state_list.c (almost every .c-file)
  tape.c, tapes.c
- removed functions which used edge_default like tapes_apply_actions_default...
- removed alphabet
- added is_in_alph() function pointer to tm
- changed old "tm_add_state" to "tm_add_state_with_default"
- added tm_add_edge_to_accept and tm_add_edge_to_reject
- written tape_actions_print
- added error_free (last time I forgot the malloc()ed err_msg - thanks to
  valgrind)
- added tm_new_with_states
- little test written
- minor changes...