Add Base64 Encode Decode in C

[rzuckerm]

To request a new code snippet, please fill out the following:

Project name: Base64 Encode Decode
Project link: https://sampleprograms.io/projects/base64-encode-decode
Language: C

[2Clutch]

Hello! I'd like to volunteer myself as tribute for this issue :)

[rzuckerm]

@2Clutch You are assigned