Add log profiler counters graphing tool

It is used to compare two different output of the log profiler : it generates graphs corresponding to the counters sampled in its output. It is going to output graph as a gnuplot script.

To run, you first need to have gnu plot installed (brew install gnuplot, sudo apt-get install gnuplot, ...), then you can simply run :
	mono compare.exe -c 7 -s "Mono GC" output1.mlpd output2.mlpd output3.mlpd

To get the command line parameters help, run :
	mono compare.exe --help