main.c: main_set_iv: use memcpy correctly
main.c: main_encrypt_pipe: fix a typo in an informational message
main: move key_salt_length, message_id_length, user_id_length into main_params
main.c: main_encrypt: write key_salt, user_id and message_id to encrypted file
main.c: finish implementing main_decrypt_pipe and main_decrypt
Makefile: decrypt: pipe password to stdin
README: Overview: mark decryption as DONE