imgtool: change getpub exporting format parameter

or `ed25519`. This will generate a keypair or private key.

To extract the public key in source file form, use

`imgtool getpub -k <input.pem> -l <lang>`, where lang can be one of `c` or

`rust` (defaults to `c`). To extract a public key in PEM form, use

`imgtool getpub -k <input.pem> -l pem`.

`imgtool getpub -k <input.pem> -e <encoding>`, where `encoding` can be one of

`lang-c` or `lang-rust` (defaults to `lang-c`). To extract a public key in PEM

format, use `imgtool getpub -k <input.pem> -e pem`.

If using AES-KW, follow the steps in the next section to generate the

required keys.

    keys.X25519.generate().export_private(path=keyfile, passwd=passwd)

valid_langs = ['c', 'rust', 'pem']

valid_langs = ['c', 'rust']

valid_encodings = ['lang-c', 'lang-rust', 'pem']

keygens = {

    'rsa-2048':   gen_rsa2048,

    'rsa-3072':   gen_rsa3072,

    keygens[type](key, password)

@click.option('-l', '--lang', metavar='lang', default=valid_langs[0],

              type=click.Choice(valid_langs))

@click.option('-l', '--lang', metavar='lang',

              type=click.Choice(valid_langs),

              help='This option is deprecated. Please use the '

                   '`--encoding` option. '

                   'Valid langs: {}'.format(', '.join(valid_langs)))

@click.option('-e', '--encoding', metavar='encoding',

              type=click.Choice(valid_encodings),

              help='Valid encodings: {}'.format(', '.join(valid_encodings)))

@click.option('-k', '--key', metavar='filename', required=True)

@click.command(help='Dump public key from keypair')

def getpub(key, lang):

def getpub(key, encoding, lang):

    if encoding and lang:

        raise click.UsageError('Please use only one of `--encoding/-e` or `--lang/-l`')

    elif not encoding and not lang:

        # Preserve old behavior defaulting to `c`. If `lang` is removed,

        # `default=valid_encodings[0]` should be added to `-e` param.

        lang = valid_langs[0]

    key = load_key(key)

    if key is None:

        print("Invalid passphrase")

    elif lang == 'c':

    elif lang == 'c' or encoding == 'lang-c':

        key.emit_c_public()

    elif lang == 'rust':

    elif lang == 'rust' or encoding == 'lang-rust':

        key.emit_rust_public()

    elif lang == 'pem':

    elif encoding == 'pem':

        key.emit_public_pem()

    else:

        raise ValueError("BUG: should never get here!")

        raise click.UsageError()

@click.option('--minimal', default=False, is_flag=True,