* HumanReadableNumber(): Simplify output for simple numbers. Examples:

HumanReadableNumber(    0.0)=      0    ---->         0
HumanReadableNumber(    0.5)=   512m    ---->       0.5
HumanReadableNumber(    0.9)= 921.6m    ---->       0.9
HumanReadableNumber(    1.0)=  1024m    ---->         1
HumanReadableNumber(   1.05)=1075.2m    ---->      1.05
HumanReadableNumber(    1.1)=    1.1    ---->       1.1
HumanReadableNumber(    1.2)=    1.2    ---->       1.2
HumanReadableNumber( 0.0e-1)=      0    ---->         0
HumanReadableNumber( 0.5e-1)=  51.2m    ---->      0.05
HumanReadableNumber( 0.9e-1)= 92.16m    ---->      0.09
HumanReadableNumber( 1.0e-1)= 102.4m    ---->       0.1
HumanReadableNumber(1.05e-1)=107.52m    ---->     0.105
HumanReadableNumber( 1.1e-1)=112.64m    ---->      0.11
HumanReadableNumber( 1.2e-1)=122.88m    ---->      0.12
HumanReadableNumber( 0.0e-3)=      0    ---->         0
HumanReadableNumber( 0.5e-3)=524.288u   ---->   524.288u
HumanReadableNumber( 0.9e-3)=943.718u   ---->   943.718u
HumanReadableNumber( 1.0e-3)=1048.58u   ---->   1048.58u
HumanReadableNumber(1.05e-3)=  1101u    ---->   0.00105
HumanReadableNumber( 1.1e-3)=1.1264m    ---->    0.0011
HumanReadableNumber( 1.2e-3)=1.2288m    ---->    0.0012

* HumanReadableNumber(): change simple printing threshold to 0.01.

* ToExponentAndMantissa(): refactor branch sequence.

Arguments shouldn't be AppendHumanReadable()-ed, they should just be shown as-is.

* fix compare script - output formatting - correctly align numbers >9999

* fix failing test (report.py); fix compare script output formatting (large numbers alignment)

This patch cleans up a number of issues with how compare_bench.py handled
the command line arguments.

* Use the 'argparse' python module instead of hand rolled parsing. This gives
  better usage messages.

* Add diagnostics for certain --benchmark flags that cannot or should not
  be used with compare_bench.py (eg --benchmark_out_format=csv).

* Don't override the user specified --benchmark_out flag if it's provided.

In future I would like the user to be able to capture both benchmark output
files, but this change is big enough for now.

This fixes issue #313.

Fixes #306

* Test bytes_per_second and items_per_second.

* Test SetLabel.

* Reformat.

* Make State::error_occurred_ private.

* Fix tests with floats.

* Merge private blocks

* fix working on mac clock_gettime

* Comment fixme

* 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

If a reporter's output stream isn't line-buffered (e.g. it's not writing
to a terminal) then it can be some time before a write to it becomes
visible.

This is problematic if, say, you're wanting to use tail -f to view the
file written to via --benchmark_out. Or if the application crashes,
leaving you with no results.

Addressed by flushing the reporters' output streams whenever we invoke
methods that may write to them.

* Cleanup the code for generating and running benchmarks

* Rework calculation of real/manual time

* Add back TSAN builder

* Refactor benchmark.cc into benchmark_register.cc and benchmark_run.cc

The benchmark.cc file is getting really big and it contains a bunch of
unrelated components. This patch separates the files into two separate
parts. The "runtime" parts and the "registration" parts.

This patch also removes the PIMPL used by Benchmark. Previously we couldn't
have STL types in the interface but now we can. Therefore there is no reason
to keep BenchmarkImp.

* add missing include

* rework windows timers again

* Guard timespec on older Windows versions

* Remove old thread safety annotation workarounds

* add additive thread range

* add test