Auto-detect whether Benchmark should produce colorized output (#126)

* Auto-detect whether to produce colorized output

Rename --color_print to --benchmark_color for consistency with the other
flags (and Google Test). Old flag name is kept around for compatibility.

The --benchmark_color/--color_print flag takes a third option, "auto",
which is the new default. In this mode, we attempt to auto-detect
whether to produce colorized output. (The logic for deciding whether to
use colorized output was lifted from GTest:
<https://github.com/google/googletest/blob/master/googletest/src/gtest.cc#L2925>.)

* Update CONTRIBUTORS, AUTHORS

CONTRIBUTORS

diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index 4bff126..33cd941 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -40,6 +40,7 @@
 Kai Wolf <kai.wolf@gmail.com>
 Lei Xu <eddyxu@gmail.com>
 Matt Clarkson <mattyclarkson@gmail.com>
+Nick Hutchinson <nshutchinson@gmail.com>
 Oleksandr Sochka <sasha.sochka@gmail.com>
 Pascal Leroy <phl@google.com>
 Paul Redmond <paul.redmond@gmail.com>