throws error for missing docs in DocTest

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>
Add test cases for ExUnit.DocTest failures
Fix regex compilation and set ucp flags
Check if ANSI escape codes are enabled on IEx's clear, closes #2441
Fix typo in GenEvent moduledoc
Merge pull request #2495 from thmzlt/patch-1

Fix typo in GenEvent moduledoc
Ensure docs with no function raise warnings
Ensure the message is not ANSI escaped

Closes #2496.
Shell info messages can still be escaped