Better logging control

[stestoll]

Currently, logging levels for some of the EasySpin functions are set via Opt.Verbosity with numerical levels 0 through 4. Logging is done by calling the private function logmsg. Here are several partially connected proposals

1. Logging could be elevated to a user-accessible function, say eslogger that can be called independently to set the log level EasySpin-wide. The legacy Opt.Verbosity could remain supported for now, or eliminated. Calling eslogger would return the currently set log level.

   eslogger(2);   % set log level
   pepper(...)   % pepper uses log level 2
   eslogger    % returns 2

   This would eliminate the need to implement log level setting interfaces separately for each EasySpin function. The log level setting would persist between EasySpin function calls. Many more EasySpin functions could support logging without needing their own interface.

2. The log levels could be named: 0 = 'off', 1 = 'info', 2 = 'detail', 3 = 'debug', 4 = 'trace'.

   eslogger detail  % = 2
   eslogger('off')  % = 0
   Opt.Verbosity = 'trace';  % = 4

3. Opt.Verbosity could be renamed to Opt.PrintLevel or similar (if not eliminated).

4. eslogger could be extended to include writing to a file, cashing all log messages, calling handler function to redirect the output to GUI, etc.

5. Maybe errors and in particular warnings can be incorporated into this as well.

[cetait]

An eslogger function that works for any subsequent EasySpin function call sounds very convenient. In the longer term, this would probably make Opt.Verbosity obsolete, after some transition period where both are supported.

I am not sure how detailed the log level needs to get, as in cases where debug level or beyond would be useful, debugging interactively may be the more common use case for the functions as they are now? I don't recall seeing any log level 4 messages in current EasySpin functions.

One aspect that may need some thought is esfit, where logging currently works a bit differently compared to the other functions, partly because in GUI mode log messages are written to the GUI log window rather than the command window. If this behavior could be handled or supported by eslogger as well, that would improve consistency. But a clear way of setting the log level would be important here, as one may want detailed logging of the results of fitting iterations, but not necessarily the same level of detail for each individual function call used for the fitting.

Writing the log output to a file could be useful for very computationally intensive calculations/fitting, and in that case incorporating warnings and errors would be important. On the other hand, such calculations may likely be run on a cluster, where command window output is typically automatically included in a log file anyway. In that case, logging to the command window alone may be sufficient. This aspect may be something where input from a wider pool of users would be useful?