Add flycheck-haskell to the extensions list
Fix argument quoting

Self-quoting keyword symbols are should be reserved for keyword
arguments and a few special cases.  Use ordinary symbols for meaningful
flags.
[Fix #305] Do not defer checks after idle timeout

This is really not necessary, because by the time this is called, there
was no change for some time, so we are unlikely to be in the middle of
an ongoing editing operation.
Wrap overlong line
Credit @bbbscarter for his help in #301 and #305
Fix typos