[#164] Use utf8-compatible codepage on Windows

Problem: xrefcheck uses utf8 symbols in reports, which are not supported
on most of Windows shells by default.
Sometimes they are printed as question marks (and it cause golden tests to fail)
and sometimes printing of them raise an error.

Solution: use function `withCP65001` from `code-page` package which
sets correct codepage on Windows and do nothing on other OSs

package.yaml

@@ -111,6 +111,7 @@ library:
     - uri-bytestring
     - yaml
     - reflection
+    - code-page
 
 executables:
   xrefcheck:

src/Xrefcheck/Command.hs

@@ -14,6 +14,7 @@ import Data.Yaml (decodeFileEither, prettyPrintParseException)
 import Fmt (blockListF', build, fmt, fmtLn, indentF)
 import System.Console.Pretty (supportsPretty)
 import System.Directory (doesFileExist)
+import System.IO.CodePage (withCP65001)
 
 import Xrefcheck.CLI (Options (..), addExclusionOptions, addNetworkingOptions, defaultConfigPaths)
 import Xrefcheck.Config
@@ -46,7 +47,7 @@ findFirstExistingFile = \case
     if exists then pure (Just file) else findFirstExistingFile files
 
 defaultAction :: Options -> IO ()
-defaultAction Options{..} = do
+defaultAction Options{..} = withCP65001 $ do
   coloringSupported <- supportsPretty
   give (if coloringSupported then oColorMode else WithoutColors) $ do
     config <- case oConfigPath of