introduce irf.log with log levels
improving irf.loh
add new function for efficient debug logging
encourage change of irf_log to irf.log
model.igrf() irf_log to irf.log
fix irf.log_debug_init
irf.log use text instead of numbers
irf_log changed to irf.log in more places
Merge branch 'devel' into irflog
Merge branch 'irflog' into devel
default log level set to warning