Use unamed tables for module compilation

* We have created a main named table that keeps all module information

* We have reduced the amount of tables by storing internal, docs and
  attributes altogether and using table looks for retriving the relevant
  information

* At this moment, creating a module in Elixir defines three tables,
  one for data, another for functions and another for clauses

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>