Implement Crockford Base32 with `encoding/base32`

[wjkoh]

Thanks for sharing this awesome project! I really enjoyed reading your blog article. I'd like to suggest using the standard encoding/base32 package for Crockford Base32 encoding, which would replace the only external dependency you have.

I've implemented Crockford Base32 in a single line of Go code, which you can find at https://gist.github.com/wjkoh/3ca6b794faf425e820ba80de777dd03d. I believe you can easily integrate this code snippet.

[jackspirou]

Thanks @wjkoh for pointing this out - great example as well, will play around with it to add in the next update.

[jackspirou]

fixed by #6