Crypto: EIP-55 support

[asladeofgreen]

Hexadecimal representations of chain addresses + digests should be checksum encoded ala EIP-55. For reference purposes the python implementation of the checksum encode/decode functions is defined here.

[asladeofgreen]

The mechanics of the encode function are as follows:

If the length of the input bytes is > 75 then simply return lower case hexadecimal, otherwise:

1. Map input bytes into an array of bits (see _bytes_to_bits_cycle function);
2. Get 32 byte blake2b hash of output of above mapping function;
3. Convert 32 byte hash into an array of 'nibbles', i.e. 4 bit numbers (see _bytes_to_nibbles function);
4. Convert array of nibbles into array of hexadecimal characters mapped from here;

[asladeofgreen]

The checksummed should also expose a set of higher-level helper encoding functions:

• encode_account_key;
• encode_block_id;
• encode_deploy_id;
• encode_digest;
• encode_signature;