Added working Pharo Smalltalk implementation [for BIP 39]

[eMaringolo]

This implementation is compliant with the spec allowing the creation of new mnemonics from an entropy from 128 to 256 bits, from mnemonic words or from the the raw entropy+checksum bytes.

Supports English, Spanish, Italian and French, and passes all tests from the Python reference implementation.

[luke-jr]

@slush0 @prusnak @voisine @ebfull

[amirziari]

not work

[k6xiao]

64位私钥导只能导出24位助记词，有的人导出12位，是怎么做到的？ The 64-bit private key can only export 24-bit mnemonics, and some people export 12-bit. How did they do it?

[prusnak]

Let's close because of https://github.com/bitcoin/bips/pull/1576

[jonatack]

Thank you, @prusnak, closing.