Consider adding parameter for enabling/disabling profiling

It would be nice if it was possible to disable profiling with just changing some package variable.
E.g.
```
PROFILING=False

@timecall(immediate=True, enabled=PROFILING)
def someFunction():
```
I assume you could in decorator just return decorated function if `enabled` is False.

Start at the timecall decorator entry point and inspect how its arguments are processed. Add an enabled option that leaves the decorated function unchanged when false, then verify that profiling remains active by default and can be disabled through a package variable as shown in the issue.

Written by the indexing model from the issue text.