Documentation: Imrpove docs for Base.

[cognivore]

I wrote something. Should add it to the repo:

@doc """
  Offensive best-effort constructor.
  You really sholdn't use this stuff because it will run Base.decode functions until one of them succeeds.
  This may not be what you want.

  Base.decode functions have the following argument:
    - `encoded` - a string to decode
    - `alphabet` - a string of characters to use as alphabet
    - `padding` - a boolean flag indicating whether to use padding or not
  `encoded` is the only required argument. It is a string to decode. For example:
  iex> Base.decode64("0L/Ri9GJIG9sb2xvINGPINCy0L7QtNC40YLQtdC70Ywg0J3Qm9CeIQ==")
  "пыщ ololo я водитель НЛО!"

  If you're interested in going the other way, check out raw_to_urlsafe and binary_to_urlsafe functions, which use Base.encode.

  We don't have default encodings for anything but b64 urlsafe.

  To unwrap `Uptight.Base` structures into a raw binary, access field `.raw`.
  To unwrap `Uptight.Base` structures into a base64 urlsafe encoded string, access field `.encoded`.
  """