Improve error checking in slice function.
Also adds a slice size of 2 by default.
Fix article not appearing.

The 'a'/'an' did not return the article which resulted in an extra
space in formatted messages.
Remove calls to debugger
Improve validation of arguments in slice function.

Some erroneous inputs produced bad result.
Add more validation - e.g. $a[1,2]

Instead of silently transforming this to $a[1], this is not validated.
Also adds Issue for deprecated use of name as type. (unused at this
point).