Make the function execution time threshold a parameter.

When using node-blocked in tests it can slow them down considerably when that threshold is to its default "10" value. By making the threshold a parameter, the value of 1 (for example) can be injected.

The change is backwards compatible and keeps the default "10 ms" when no options are specified.

Release 1.1.0

Release 1.0.0

Release 0.0.1