Promote flycheck-color-mode-line.el [#119]

Great work by @syl20bnr
Wrap overlong line
Copy-edit syntax checker docstrings

Improve consistency and wording
Defer syntax checks while a buffer is being reverted
Try hard to perform deferred syntax checks

Try to run deferred syntax checks after each command in a buffer.  With
pending deferred checks, error information in the current buffer is
already outdated, so we should restore it asap.