Fix for Private Key (WIF-Compressed)

When testing with a `private_key = '0000000000000000000000000000000000000000000000000000000000000001'` instead of `private_key = bitcoin.random_key()`,
the generated Private Key (WIF-Compressed) is wrong `5HpHagT65TZzG1PH3CSu63k8DbpvD8s5ip4nEB3kEsrefhvB5QZ`, it should be `KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn`. As it turns out, the proper way to get the correct compressed WIF is to pass `'wif_compressed'` and not `'wif'` to the `bitcoin.encode_privkey` function, as pointed out in the Main.py from the bitcoin python package.

```
def encode_privkey(priv, formt, vbyte=0):
    if not isinstance(priv, int_types):
        return encode_privkey(decode_privkey(priv), formt, vbyte)
    if formt == 'decimal': return priv
    elif formt == 'bin': return encode(priv, 256, 32)
    elif formt == 'bin_compressed': return encode(priv, 256, 32)+b'\x01'
    elif formt == 'hex': return encode(priv, 16, 64)
    elif formt == 'hex_compressed': return encode(priv, 16, 64)+'01'
    elif formt == 'wif':
        return bin_to_b58check(encode(priv, 256, 32), 128+int(vbyte))
    elif formt == 'wif_compressed':
        return bin_to_b58check(encode(priv, 256, 32)+b'\x01', 128+int(vbyte))
    else: raise Exception("Invalid format!")
```

The fix can be done in a couple ways:

`bitcoin.encode_privkey(bitcoin.decode_privkey(compressed_private_key, 'hex'), 'wif')` -> 5HpHagT65TZzG1PH3CSu63k8DbpvD8s5ip4nEB3kEsrefhvB5QZ (WRONG)

`bitcoin.encode_privkey(bitcoin.decode_privkey(compressed_private_key, 'hex'), 'wif_compressed')` -> KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU9FMLM39zT (WRONG)

`bitcoin.encode_privkey(bitcoin.decode_privkey(compressed_private_key, 'hex_compressed'), 'wif_compressed')` -> KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn (CORRECT)

`bitcoin.encode_privkey(bitcoin.decode_privkey(private_key, 'hex'), 'wif_compressed')` -> KwDiBf89QgGbjEhKnhXJuH7LrciVrZi3qYjgd9M7rFU73sVHnoWn (CORRECT)

code/key-to-address-ecc-example.py

@@ -21,7 +21,10 @@ print("Private Key Compressed (hex) is: ", compressed_private_key)
 
 # Generate a WIF format from the compressed private key (WIF-compressed)
 wif_compressed_private_key = bitcoin.encode_privkey(
-    bitcoin.decode_privkey(compressed_private_key, 'hex'), 'wif')
+    bitcoin.decode_privkey(compressed_private_key, 'hex_compressed'), 'wif_compressed')
+# also can be done correctly with
+#wif_compressed_private_key = bitcoin.encode_privkey(
+#    bitcoin.decode_privkey(private_key, 'hex'), 'wif_compressed')
 print("Private Key (WIF-Compressed) is: ", wif_compressed_private_key)
 
 # Multiply the EC generator point G with the private key to get a public key point