Add error filter to increment columns

For use with syntax checkers that emit zero-based columns
Update error filter API docs
Fix pylint error columns
fixup! Add error filter to increment columns
Document base index of error colums in Flycheck
Add test for GHC error to verify GHC error columns
[Fix #536] Merge branch 'clarify-error-columns'

* clarify-error-columns:
  Add test for GHC error to verify GHC error columns
  Document base index of error colums in Flycheck
  fixup! Add error filter to increment columns
  Fix pylint error columns
  Update error filter API docs
  Add error filter to increment columns
Add support for language test selector