Kernel.Typespec will be responsible for handling typespec
logic during compilation, such as definitions, conversion to
Erlang and warnings. Its API shall never be public.
Code.Typespec will handle the runtime aspects, such as reading
from .beam files and conversion back to Elixir AST. Its API
may be made public in the future but it is currently private.
This PR also simplifies definition of typespecs internally by
avoiding multiple macro passes and speeds up typespec processing
on OTP 20+ by skipping the translation pass from Elixir to Erlang.
The test suite was also reorganized and made async: true.
José Valim
4f14aea9f6