Linting integration

This commit brings in an HLint configuration file
and several recommended modifications such as:

* End-of-line extra spaces removal;
* Import lines ordering;
* Redundant $ removal;
* Generalisation of ++ and map to <> and fmap;
* Preferring `pure` over `return`;
* Removing extraenous extensions.

And finally, a `stylish-haskell` helper script
that detects if code files are dirty. Can be useful for CI,
although manually calling it can be nice if you would rather
first implement then beautify.

src/Hash2Pub/Main.hs

@@ -1,10 +1,10 @@
 module Main where
 
-import System.Environment
-import Data.IP (IPv6, toHostAddress6) -- iproute, just for IPv6 string parsing
-import Control.Concurrent
+import           Control.Concurrent
+import           Data.IP            (IPv6, toHostAddress6)
+import           System.Environment
 
-import Hash2Pub.FediChord
+import           Hash2Pub.FediChord
 
 main :: IO ()
 main = do
@@ -20,12 +20,12 @@ main = do
     -- idea: list of bootstrapping nodes, try joining within a timeout
     -- stop main thread from terminating during development
     getChar
-    return ()
+    pure ()
 
 readConfig :: IO FediChordConf
 readConfig = do
     confDomainString : ipString : portString : _ <- getArgs
-    return $ FediChordConf {
+    pure $ FediChordConf {
         confDomain = confDomainString
       , confIP = toHostAddress6 . read $ ipString
       , confDhtPort = read portString