Add tracing support

[XVilka]

To be able to trace Python code (including limp.py) with this module: https://docs.python.org/3.6/library/trace.html

[dbousque]

Hi @XVilka , you can certainly already use trace with lymp, since you can execute any arbitrary Python code using it, unless I'm missing something ? :)

[XVilka]

Yes, just modified the limp.py. Thought there are may be a better ways for seamless tracing/debugging.