Fixed doc typos in Kernel.Special_Forms
Fixed doc typos in ExUnit
Fixed doc typos in ExUnit.Assertions
Fixed doc typos in ExUnit.DocTest
Fixed docs as recommended by @alco
Remove unused test_helper project configuration from mix
Merge pull request #1429 from jwarwick/ex_unit_docs

Fixed doc typos in ExUnit
Merge pull request #1427 from jwarwick/doc_typos

Fixed doc typos in Kernel.Special_Forms
Improve use of operator has no effect messages, closes #1431