main.c: fix a typo in a message string
main.c: improve message text
README: Development: declare C standard
main: write sizeof(size_t) and ciphertext length to ciphertext file
main.c: close ciphertext and plaintext files
main.c: main_encrypt: report success at the end
main: begin main_decrypt implementation
main.h: fit lines into 80 columns
Makefile: rename default to encrypt
Makefile: add decrypt
.gitignore: update to reflect Makefile