main_params: replace size_max with size_max_digits, change size_t_format semantics, add size_t_flex
main_write_char(): create an entire string and the write it in one operation
main_encrypt_pipe(): fix compiler warning about ciphertext_total type
main_decrypt_pipe(): update written byte progress in place
remove main_write_size_t()
Makefile: main: add main.h to dependencies