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