fio2gnuplot: Adding 2D graphs for each fio trace

When tracing multiple files, the 3D graph is useful to understand the
behavior of a group of disks but makes difficult to understand how a
particular disk behave during the test.

This patch does add three 2D plots for each fio trace :
- the 2D Raw tracing
This plot is the exact plotting of the raw values reported by fio.
It's very precise but hard to read when having many many traces

- the 2D Smooth tracing
This plot is a smooth version of the raw tracing. It tries to keep as
much as possible a tracing close to the raw one but makes it more
readable by aggregating points.

- the 2D Trend tracing
This plot is trying to setup a trend of the global performance. It
aggregates many points and hide peaks. It only consider at giving a very
easy to understand plotting on how the bench was performing.
It's much more easier to read but could be misleading if raw or smooth
tracing didn't got read before.
fio2gnuplot: Adding sample files

This commit does add some sample log files and makefile to use
fio2gnuplot. This is very useful for understanding, developping or testing fio2gnuplot.

A simple "make" will do the job for you.