Add doc-test testsuite, fixing doc examples

test/DocTestMain.hs

@@ -0,0 +1,16 @@
+module Main where
+
+import System.Environment
+         ( getArgs )
+import Test.DocTest
+         ( mainFromLibrary )
+import Test.DocTest.Helpers
+         ( extractSpecificCabalLibrary, findCabalPackage )
+
+main :: IO ()
+main = do
+  args <- getArgs
+  pkg  <- findCabalPackage "regex-tdfa"
+  -- Need to give the library name, otherwise the parser does not find it.
+  lib  <- extractSpecificCabalLibrary Nothing pkg
+  mainFromLibrary lib args