[PATCH] rename strn*() macros to strmax

[PATCH] rename strn*() macros to strmax

Hey, I wrote the strn*() macros just 10 days ago and yesterday this trap
caught me with the %c{x} bug.
The names are misleading cause we all expect that the from field is limited by
the size argument, but we actually limit the overall size of the destination
string to prevent a overflow.

Here we rename all strn*() macros to str*max(). That should be
more self-explanatory.