Add some mechanism for distinguishing between $xll and XLOG_LEVEL such
that we can have a different prefix for each style, this would allow
for instance that $xll type log calls could give detailed information
about where in the program code the log was called and an additional
step back up the stack stracem to see where the current sub was called
from (the sub in which the log call is made)


Possibly add filtering for log calls with log levels that are below
the threshold for output at the time of compilation. Say for instance
that the environment variable LOG_LEVEL is set to 'WARN'. At program
startup, the internal log level will be set to WARN. Should we at this
poing filter out any log calls at levels below WARN? Or, should we
allow for the possibility that withing the program the log_level
setting could be changed somewhere, thereby allowing, for instance,
INFO, log calls to achieve output.


Add in some mechanism for log rotation. I'm sure there is an
appropriate log rotatoin package out there.


Add in some mechanism for a configuration file, with options like
logging inside of specific packages under certain circumstances,
etc...


Also, maybe add something so that different log levels may be
associated with different filehandles. For instance, ERROR could be
bound to STDERR, while INFO could be bound to STDOUT, etc.


It would be great to figure out how to use the FILTER to actually find
the closing paren on the log call rather than forcing log calls that
are to be filtered to exist all on one line


need to change exported log_level constants to be prefixed with
LL_<LEVEL> or some such