This is secretly just a test commit to get appveyor to run again.

VC 2013 injects valid when  assigning an initializer list to std::set.
This attempts to work around this issue by using std::set's constructors
instead of the assignment operators.

* Support multiple ranges in the benchmark

google-benchmark library allows to provide up to two ranges to the
benchmark method (range_x and range_y). However, in many cases it's not
sufficient. The patch introduces multi-range features, so user can easily
define multiple ranges by passing a vector of integers, and access values
through the method range(i).

* Remove redundant API

Functions State::range_x() and State::range_y() have been removed. They should
be replaced by State::range(0) and State::range(1).
Functions Benchmark::ArgPair() and Benchmark::RangePair() have been removed.
They should be replaced by Benchmark::Args() and Benchmark::Ranges().

* Add RegisterBenchmark

* fix test inputs

* fix UB caused by unitialized value

* Add RegisterBenchmark

* fix test inputs

* fix UB caused by unitialized value

* Work around GCC 4.6/4.7/4.8 bug

These options allow you to write the output of a benchmark to the specified
file and with the specified format. The goal of this change is to help support
tooling.

GCC 4.6 doesn't provide std::chrono::steady_clock and GCC 4.7 doesn't provide
std::this_thread::sleep_for. I would prefer to support GCC 4.7 but I'm
reverting this since the bots are GCC 4.6.

This reverts commit c5f45495.

GCC 4.7 doesn't provide std::this_thread::sleep_for on my system.
This patch changes the tests to use a different method for wasting
cycles.

Without these, clang reorders these instructions as if they were
regular loads/stores which causes SIGILL from the kernel because
it performs all the loads before it starts testing the values.

This implementation is less likely to ICE compilers, and is more correct.
It also acts as a memory barrier which will help prevent writes to global memory
from being optimized away.

Add policy CMP0056, which honors the link flags in try_compile and
try_run. This allows for building against non-system libc++ by providing
the correct -L and rpath options in a containing project.

For example:

    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -L ${LLVM_ROOT}/lib -l c++ -l c++abi")
    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,-rpath,${LLVM_ROOT}/lib")

Add `state.SetComplexityN(state.range_x());` to documentation so that complexity is calculated correctly.

Merge branch 'added_lambdas' of git://github.com/ismaelJimenez/benchmark into ismaelJimenez-added_lambdas