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/args.rs

@@ -571,6 +571,11 @@ impl Args {
         self.mmap
     }
 
+    /// Whether ripgrep should be quiet or not.
+    pub fn quiet(&self) -> bool {
+        self.quiet
+    }
+
     /// Create a new printer of individual search results that writes to the
     /// writer given.
     pub fn printer<W: Terminal + Send>(&self, wtr: W) -> Printer<W> {
@@ -580,7 +585,6 @@ impl Args {
             .eol(self.eol)
             .heading(self.heading)
             .line_per_match(self.line_per_match)
-            .quiet(self.quiet)
             .null(self.null)
             .with_filename(self.with_filename);
         if let Some(ref rep) = self.replace {
@@ -660,6 +664,7 @@ impl Args {
             .eol(self.eol)
             .line_number(self.line_number)
             .invert_match(self.invert_match)
+            .quiet(self.quiet)
             .text(self.text)
     }
 
@@ -679,6 +684,7 @@ impl Args {
             .eol(self.eol)
             .line_number(self.line_number)
             .invert_match(self.invert_match)
+            .quiet(self.quiet)
             .text(self.text)
     }