Benchmark: Measure the time that PHP scripts take to execute

This class can measure the time it takes to execute each parts of a PHP script.

The class can take note of different check points of the current script and thet time that elapsed since the start. Then it can generate an HTML report that show various types of statistics.

Features:

* Assign a mark to a check point in part of the code with a call level depth (for function calls)
* Compute the time between two check points for the different levels
* Show the slowest parts of the code using a color codes from green to red
* Can use an external data, for example, the number of SQL queries to show the slowest queries