Be better with short circuiting with --quiet.

It didn't make sense for --quiet to be part of the printer, because --quiet
doesn't just mean "don't print," it also means, "stop after the first
match is found." This needs to be wired all the way up through directory
traversal, and it also needs to cause all of the search workers to quit
as well. We do it with an atomic that is only checked with --quiet is
given.

Fixes #116.

src/search_buffer.rs

@@ -81,6 +81,13 @@ impl<'a, W: Send + Terminal> BufferSearcher<'a, W> {
         self
     }
 
+    /// If enabled, don't show any output and quit searching after the first
+    /// match is found.
+    pub fn quiet(mut self, yes: bool) -> Self {
+        self.opts.quiet = yes;
+        self
+    }
+
     /// If enabled, search binary files as if they were text.
     pub fn text(mut self, yes: bool) -> Self {
         self.opts.text = yes;
@@ -104,7 +111,7 @@ impl<'a, W: Send + Terminal> BufferSearcher<'a, W> {
                 self.print_match(m.start(), m.end());
             }
             last_end = m.end();
-            if self.printer.is_quiet() || self.opts.files_with_matches {
+            if self.opts.stop_after_first_match() {
                 break;
             }
         }