This patch does two things:

1. It overhalls the static initialization in Walltime to be simplier. It uses
   a static variable inside WallTime::Now() to initialize the timer.

2. Add a logging mechanism so that the -v flag actually has meaning and
   reimplement the CHECK macros to allow extra messages to be streamed in.

This patch cleans up our use of generic macros and also merges changes in the
build system.

It adds options -DBENCHMARK_ENABLE_TESTING and -DBENCHMARK_ENABLE_SHARED.

libstdc++'s std::regex has (or had) a bug in std::regex::operator=(...) that
caused undefined behaviour. Clang will detect this and compile the function so
that it crashes at runtime. This patch tried to detect that bug during
configuration.

Add _build to gitignore to enable out-of-source builds

Fix #77 build on freebsd 10

One more 64-bit to 32-bit conversion

Fix #72 by avoiding 64-to-32-bit shortenings

Using Travis CI.

Use #ifdef to protect calling Factorial in benchmark_test.cc

Added Travis build status badge.

Remove CHECK_* from public API.

Fixes #65

CHECK_* are now private and used internally in the library. The test
uses have been replaced with asserts.

Fixes #62.

added googletest dependency to tests (allows compilation with -j)

Turn the global mutex into instance variables

Fix #50 by using nullptr and adding stricter warning.

Fix #54 by correcting reference to CXX flags for variants.

Move pthread dependency to test CMakeLists.txt

To fix #52