Makefile: Link libcrypto to executables
Add apl_crypt header & source

Added encryption method, plaintext=>ciphertext with a given cipher
context EVP_CIPHER_CTX. Also added a crypt test, which will be
used to check that the original plaintext and the decrypted
plaintext match.

plain => cipher
ciphter => plain2
assert(plain == plain2)
apl_crypt: Add apl_decrypt function

crypt test now ensures the original plaintext and decrypted plaintext
match, using strncmp