Compilation passes --pedantic and -Wall
Better output
Removed trailing whitespace
Added makefile
Split into files
Added .gitignore
Fixed example
Made block encryption/decryption private
Changed int to size_t where appropriate
Added support for size prediction

When pointer to buffer to fill is NULL, do the decrypting/encrypting in memory
only and return buffer size that user should allocate for actual
decryption/encryption.