Handles generating a token:

Tokens are broken up into several components:

• version: v1 or v2 -- v2 suggested
• purpose: Local or Public -- Local -> Symmetric Encryption for payload & Public -> Asymmetric Encryption for payload
• payload: A signed or encrypted & b64 encoded string
• footer: An optional value, often used for storing keyIDs or other similar info.

Examples:

iex> {:ok, pk, sk} = Salty.Sign.Ed25519.keypair()
iex> keypair = {pk, sk}
iex> token = generate_token("v2", "public", "This is a test message", keypair)
"v2.public.VGhpcyBpcyBhIHRlc3QgbWVzc2FnZSe-sJyD2x_fCDGEUKDcvjU9y3jRHxD4iEJ8iQwwfMUq5jUR47J15uPbgyOmBkQCxNDydR0yV1iBR-GPpyE-NQw"
iex> Paseto.parse_token(token, keypair)
{:ok,
  %Paseto.Token{
  footer: nil,
  payload: "This is a test message",
  purpose: "public",
  version: "v2"
  }}

@spec parse_token(String.t(), binary()) :: {:ok, Paseto.Token} | {:error, String.t()}

Handles parsing a token. Providing it just the entire token will return the Paseto.Token struct with all fields populated.

Examples:

iex> token = "v2.public.VGhpcyBpcyBhIHRlc3QgbWVzc2FnZSe-sJyD2x_fCDGEUKDcvjU9y3jRHxD4iEJ8iQwwfMUq5jUR47J15uPbgyOmBkQCxNDydR0yV1iBR-GPpyE-NQw"
iex> Paseto.parse_token(token, keypair)
{:ok,
  %Paseto.Token{
    footer: nil,
    payload: "This is a test message",
    purpose: "public",
    version: "v2"
  }}