Let users specify full path to output files

[alexdewar]

Following #513, users can specify the output folder via the command line, but the output file name still must be set in the config file. It might be useful to let users set the full path to output folders via the command line.

The problem is that each run of the program produces many output files. The current solution to this is to allow a placeholder string {TIMESTAMP} in the file name specified in the config file, which is expanded to the current timestamp whenever an output file is created. We could apply this exact same mechanism to a command-line argument, however as curly braces are special characters in bash (not sure about powershell), users would have to know to escape them, so this could prove to be a bit of a footgun.

[jamesturner246]

Not sure it's any better, but what if we just omit the curly braces? Or even dunder...

something__TIMESTAMP__something