Rename the error message popup buffer

Frees the name `*Flycheck errors*` for the new listing buffer
Add function to format an error as string
Work around dash bug

s-lex-format from dash.el fails, if the replacement text contains a
literal backslash, see magnars/s.el#34
Add a command to determine the Flycheck version
Track the checker that reported an error
Add `flycheck-error-format` to the manual
Add `flycheck-list-errors` to list all errors
Fix compilation warning
Merge branch 'error-listing'

* error-listing:
  Fix compilation warning
  Add `flycheck-list-errors` to list all errors
  Add `flycheck-error-format` to the manual
  Track the checker that reported an error
  Add a command to determine the Flycheck version
  Work around dash bug
  Add function to format an error as string
  Rename the error message popup buffer