#51: (E)WIF: add four methods: devine format, allow passing to the f() an hexadecimal string

• which will devine if it’s an WIF or an EWIF format.
• allow (E)WIF imports from string parameter in hexadecimal rather than from file.
• from_wif_or_ewif_file()
• from_wif_or_ewif_hex()
• from_wif_hex()
• from_ewif_hex()