Add missing module and function docs

[juanhurtado10]

Context

Elixir treats documentation as a first-class citizen. This means documentation should be easy to write and read to everyone.

Objective

• To set a documentation standard for the library.
• To add missing modules and functions docs for all the XDR types.
• To improve the current docs

References

• https://guides.github.com/features/mastering-markdown/
• https://elixirschool.com/es/lessons/basics/documentation/
• https://hexdocs.pm/elixir/1.12/writing-documentation.html

Format

defmodule Greeter do
  @moduledoc """
  ...
  """

  @doc """
  Prints a hello message

  ## Parameters

    - name: String that represents the name of the person.

  ## Examples

      iex> Greeter.hello("Sean")
      "Hello, Sean"

      iex> Greeter.hello("pete")
      "Hello, pete"

  """
  @spec hello(String.t()) :: String.t()
  def hello(name) do
    "Hello, " <> name
  end
end