Buffet: utility function tweaks

Various tweakes to helper functions and classes, split off from
a larger CL that required them.

1. Added Error::AddToPrintf to help add formatted error messages.
2. Added Error::GetFirstError to get the innermost error occurred.
3. Added string_utils::ToString and swept code using std::to_string
   in order to ensure we format doubles correctly (using %g instead
   of %f format specifier) and bool values (using "true"/"false"
   instead of 1/0).
4. Fixed C-style cast in http_utils.h and using static_cast now.
5. Fixed a few linter warnings. Also since the linter was updated
   there is no reason to have some NOLINT since many C++11 features
   are now recognized properly by cpplint.

BUG=None
TEST=All unit tests pass.

Change-Id: I208ffaa3f0ec0a5ff78bf9e8151e784ec8cd77e2
Reviewed-on: https://chromium-review.googlesource.com/202962
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>

buffet/http_request.h

diff --git a/buffet/http_request.h b/buffet/http_request.h
index 8aedc45..e5b9710 100644
--- a/buffet/http_request.h
+++ b/buffet/http_request.h
@@ -5,6 +5,7 @@
 #ifndef BUFFET_HTTP_REQUEST_H_
 #define BUFFET_HTTP_REQUEST_H_
 
+#include <limits>
 #include <map>
 #include <memory>
 #include <string>
@@ -303,7 +304,7 @@
   // range_value_omitted is used in |ranges_| list to indicate omitted value.
   // E.g. range (10,range_value_omitted) represents bytes from 10 to the end
   // of the data stream.
-  const uint64_t range_value_omitted = (uint64_t)-1;
+  const uint64_t range_value_omitted = std::numeric_limits<uint64_t>::max();
 
   DISALLOW_COPY_AND_ASSIGN(Request);
 };