Change the available Benchmark options

Fix and improve BENCHMARK macros.

Fix #96: Prevent times from being negative.

The calculation was actually inside the loop for a reason.

This reverts commit 47442b90.

Add variadic macro for BENCHMARK_TEMPLATE in c++11 and beyond.

I didn't mean to commit this to master.
This reverts commit b7d03ac4.

Add JSON Reporter

Apply reporter interface changes.