Encodes and decodes Ascii85.

Ascii85, also called Base85, is a form of binary-to-text encoding developed by Paul E. Rutter.

It uses five ASCII characters to represent four bytes of binary data (making the encoded size 1⁄4 larger than the original, assuming eight bits per ASCII character).

For encoder:
$ gcc encasc85.c -o encasc85

For decoder:
$ gcc decasc85.c -o decasc85

For encoding example.txt:
$ ./encasc85 < example.txt

For decoding example.txt:
$ ./decasc85 < example.txt