Added Python versions of base64 examples

These are transliterations of the existing C files.
They're not particularly Pythonic or performant, but they're a start.

Example of usage

```
$ echo '  YW55IGNhcm5hbCBwbGVhcw==' | PYTHONPATH=../build/opt/src/bindings/python/ python base64.py
inputsize=27
input=  YW55IGNhcm5hbCBwbGVhcw==
((((89L, 87L, 53L, 53L), (73L, 71L, 78L, 104L), (99L, 109L, 53L, 104L), (98L, 67L, 66L, 119L), (98L, 71L, 86L, 104L)), (99L, 'w', '=', '=')),)
$ echo '  YW55IGNhcm5hbCBwbGVhcw==' | PYTHONPATH=../build/opt/src/bindings/python/ python base64_sem1.py
inputsize=27
input=  YW55IGNhcm5hbCBwbGVhcw==
(97L, 110L, 121L, 32L, 99L, 97L, 114L, 110L, 97L, 108L, 32L, 112L, 108L, 101L, 97L, 115L)
$ echo '  YW55IGNhcm5hbCBwbGVhcw==' | PYTHONPATH=../build/opt/src/bindings/python/ python base64_sem2.py
inputsize=27
input=  YW55IGNhcm5hbCBwbGVhcw==
(97L, 110L, 121L, 32L, 99L, 97L, 114L, 110L, 97L, 108L, 32L, 112L, 108L, 101L, 97L, 115L)
```