lzw: Rename a bunch of structures, functions and variables.
lzw: Rename a bunch of structures, functions and variables.

    new_code              -> code
    last_value            -> value
    first_value           -> first
    previous_entry        -> extends
    current_entry         -> table_size
    previous_code         -> prev_code
    previous_code_first   -> prev_code_first
    current_code_size     -> code_size
    current_code_size_max -> code_max
    lzw__next_code        -> lzw_read_code

jcupitt/libvips,jcupitt/libvips,lovell/libvips,jcupitt/libvips,lovell/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips