Rename y_post_increment_***transaction() to y_increment_...() etc.

The old _post_ variants still exist, but I'm deprecating them because I think those names don't make sense.
Add y_get_current_time() and y_delay_until()

These are handy for, say, delaying ramp up by an hour to give some time for the other users to finish setting up their test data.
Also makes y_think_time_for_rampup_ext() use y_get_current_time()
Remove y_timestamp.

We've come a long way since this ancient stuff got checked in ..
Remove some old commented-out code.
Add a config file to generate doxygen source documentation with.
Tweaking the doxygen config a bit.
Tell git to not track the html folder we will be using for doxygen output.
Add the Y_DELAY_ONCE() macro.
Move the GPL license text to the doc/ directory.
Make the content of README.md the main index file for doxygen
Rename Y_DELAY_ONCE() to y_delay_once()

Let's stop screaming.
The end user doesn't actually need to know it's a macro.
Add a layout file to the doxygen setup and move the doxygen warnings up into the 'doc' folder.
Fix a ton of doxygen warnings caused by use of \start_example and \end_example tags.

Seems to me those tags got removed by doxygen at some point. Hrm.
Update the y_setup() documentation to reflect reality more accurately.
Fix the last doxygen warnings by adding \code tags to the vts error reporting function.

Also updates the documentation a bit, while were at it.
Remove the doxygen warning logfile.

Since it's now empty (and we want it to stay that way) having doxygen report them on stdout/stderr instead is fine.
Update the y_malloc() documentation so that it actually works.