Upgrade Luerl

[manuel-rubio]

Looks like github.com/luerl evolved at some point including by default Elixir modules, but also changing the name of the functions. Not sure if the internal behaviour could be affected so, in this ticket I guess could be great idea:

1. Upgrade luerl
2. Change the use of :luerl module to use Luerl
3. Check the use of the functions because :luerl.set_table/3 and :luerl.eval/2 doesn't exist anymore. I guess they were renamed to :luerl.set_table_keys/3 so we could use Luerl.set_table_keys/3 and :luerl.eval/2 was renamed to :luerl.do/2 so we could use Luerl.do/2.
4. Make tests!

Yes, I know, there are no enough tests, but it's something we have to change :-)

[manuel-rubio]

It appears that Luerl version 1.4 isn't 100% compatible with the old one, and scripts created with the previous version are now broken. I'll review it later (maybe in one or two months).