Add support for negative array indexes (from end)

[olivr70]

[//]:

Is your feature request related to a problem? Please describe. To get the name of folder for a note, I currently use `reverse(split(file.path, "/"))[1]

Describe the solution you'd like I would like to able to write

split(prop)[-1] to get the last item 

Describe alternatives you've considered I currently use the code above reverse(split())

[holroy]

If #2238 is accepted, you'll be able to do slice(split(prop), -1) to do just this.