[Qt-creator] Macros for profiling

[Nikolai Kosjar]

Hiya!

I want to introduce some simple macros for profiling:

	https://codereview.qt-project.org/#change,49842
	WIP, Documentation/Examples included

Basically, there are macros that record how often and how long an object 
existed on the stack and macros that just log the elapsed time since 
previous log calls.

By default, profiling support is disabled (it is a #define in 
utils/profiler.h) and thus the macros expand to nothing.

If you have objections or further suggestions, just step up :)

How to use:

0. Link against libUtils in your project where necessary
    (mostly it's already linked)
1. Explicitly enable profiling support in utils/profiler.h.
2. Add "#include <utils/profiler.h>" to the relevant files and 
instrument your code with the Macros (see examples in the doc)
3. Compile & Run Qt Creator - depending on the used macros some output 
might be generated during run time.
4. Quit Qt Creator - on shutdown a summary is printed.

Motivation:

1. With this, you can create a patch of your instrumented code and send 
it your colleague in order to compare the resulting numbers. Of course, 
this becomes superfluous from the point a cross platform profiler with 
easy sharing of the instrumentation appears.

2. I plan to use some macros in the auto and plugin tests since lately 
there were some performance slowdowns in e.g. the C++ Support area. The 
profiling output can be also written to a log file. Having some 
"reference" output for certain tests would certainly be quite nice when 
reviewing patches that deal with template instantiations etc... I know 
there is QBENCHMARK(_ONCE), but I would prefer to have the profiling 
output on demand and besides this does not solve point 1 in a broader sense.

Nikolai