Add base64 module

[S-YOU]

• Only import _struct as struct changes to this one.

% make run 
import base64
encoded = base64.b64encode('data to be encoded')
print encoded
data = base64.b64decode(encoded)
print data

ZGF0YSB0byBiZSBlbmNvZGVk
data to be encoded

[trotterdylan]

Great! Thanks for doing this! Merging.