Add Google Analytics tracking code
Mention that it does not work on MinGW
Update configure checks
Do not check for atexit()

It is not used anymore.
Fix UT_DEFAULT_MAIN
Undeprecate UT_DEFAULT_MAIN

If the system does not support main as a weak symbol, it is necessary to
include this macro (or write custom main).
Improve UT_DEFAULT_MAIN

Now it only calls a helper function that does all the work. The weak
entry point also delegates everything to this function, so that the code
is not duplicated.
Update README
Add possibility to control colors
Add long option or customizing coloring
Control quieting in putc_color

This helps by moving the check to only one place.
Document color controls