Minor changes in comments
Robustness + check if tmp dir exists

Overall robustness to paths containing spaces improved
In create_lock_folder(): switch -p not used anymore when creating the
"running scripts folder" (i.e. current folder must already exist)
Increased log verbosity in run_main()
Robustness in case of bad log file path

Detect bad log file path or name, and echo the detected issue to give
guidance to the user, how to solve the issue
Fixes #9

Inside script: change directory to the directory of the script.
As a consequence, the scripts can be called from anywhere, even if the
paths defined in the config.sh file are relative