Extract most shared logic into SimplePrinter

This should hopefully allow for more command line options, like no
color, omitting line number and file names for better scriptability.

src/filematch.rs

@@ -9,8 +9,11 @@ pub struct FileMatch {
 
 impl FileMatch {
     pub fn print(&self, config: &Config) {
-        let cp = ColorPrinter {};
-        cp.print(&config, &self);
+        let cp = ColorPrinter {
+            config: config,
+            file_match: self,
+        };
+        cp.print();
     }
 }