Add support for ternary operator and logical expressions

[gsouf]

Hi,

This fix makes the getKey to be replaced with getKeys that is now able to return multiple keys at once. That way we can add support for logical expressions and ternary operators that required the ability to return multiple keys.

Fix #39

[gsouf]

Closing as maintainer doesnt plan to get this fixed.

[gsouf]

@oliviertassinari concerning travis failing for some reasons the eslints does not run the same way on my computer and on travis, getting it fixed to match travis way

[oliviertassinari]

@gsouf Thanks

[gsouf]

Thank you!