Parallelize search

Why?
====

Searching hundreds or thousands of tokens with ag can be slow; this
introduces parallel processing of search so results are returned more
quickly.

src/Unused/CLI/ProgressIndicator.hs

@@ -5,6 +5,7 @@ module Unused.CLI.ProgressIndicator
     , progressWithIndicator
     ) where
 
+import Control.Concurrent.ParallelIO
 import Unused.CLI.Util
 import Unused.CLI.ProgressIndicator.Types
 import Unused.CLI.ProgressIndicator.Internal
@@ -23,6 +24,6 @@ progressWithIndicator :: (a -> IO [b]) -> ProgressIndicator -> [a] -> IO [b]
 progressWithIndicator f i terms = do
     printPrefix i
     indicator <- start i $ length terms
-    concat <$> sequence (ioOps indicator) <* stop indicator
+    concat <$> parallel (ioOps indicator) <* stop indicator <* stopGlobalPool
   where
     ioOps i' = map (\t -> f t <* increment i') terms

unused.cabal

@@ -42,6 +42,7 @@ library
                      , terminal-progress-bar
                      , ansi-terminal
                      , unix
+                     , parallel-io
   ghc-options:         -Wall -Werror -O2
   default-language:    Haskell2010