unify error messages, save memory

[rurban]

Currently the error messages are customized to include the function name as prefix, and the argument name.
This is great for the user, but most likely memory overkill.
Normal libc's have a unique error message per number, stored globally only once. Not 100x times.

Measure the memory impact.
possibly convert to unified strings
or to fprintf("%s: %s message", __FUNCTION__, "dest"), so we can share at least the base message.

[rurban]

Measured the impact: with the new errorhandling code and global errmsg table we need 30kb more,
and measuring the win with massif on the 4 so far changed unit tests measured so memory win at all.
given that the error messages degraded, it is rejected. I'll keep the branch errmsg-gh19 though

changed funcs for testing: vsnprintf_s, vsprintf_s, swprintf_s, vswprintf_s

massif test script: (darwin)

make all
test -f src/.libs/libsafec-3.0.3.dylib && strip -S src/.libs/libsafec-3.0.3.dylib
make -C tests t_vsprintf_s
strip -S tests/t_vsprintf_s
valgrind --tool=massif --massif-out-file=massif tests/t_vsprintf_s
grep -h mem_heap_B= massif | cut -c12-|sort -rn|head -n1

# 190515 errmsg
# 190515 sprintf