[#1] get/[2,3] to access values in nested maps.
[#1] Renamed to ktn_maps. Added tests.
[#1] Error for get/2, default value for get/3.
Merge pull request #2 from inaka/jfacorro.1.katana.maps

[#1] get/[2,3] nested maps.
Merge pull request #9 from inaka/master

get/[2,3] to access values in nested maps