Assignment for week 6: The goal is to implemennt a simple tool for
symmetric encryption of a file with OpenSSL.

Deadline: November 17, 2020 (8:00 AM), maximum is 10 points.

Create a simple program that encrypts and decrypts an arbitrary file with
AES-128 in CBC mode (using OpenSSL library) with

  fixed key: 00112233445566778899aabbccddeeff (in hexa) and
  fixed IV:  00000000000000000000000000000008 (in hexa).

Your submitted archive (zip or tar) should contain one C program (and Makefile).

Hints:

 - File names (input, output) and command (encrypt, decrypt) should be taken
   from command line arguments.

 - To access the file, you can use OpenSSL BIO functions or any other functions
   (you can use a file buffer for the whole file in memory; test files will
   be up to 64 MiB in size).

 - Properly handle errors. The file can be empty or not accessible;
   memory allocation can fail etc.

 - Do NOT use padding. The encrypted file MUST be the same size as the input.
   Input file size must be aligned to cipher encryption blocks
   (see EVP_CIPHER_CTX_set_padding).
   If the file is not aligned, fail the operation and print an error.

The source code must be compilable on the provided virtual machine (Linux Fedora)
or on aisa server.