Added DeleteDuplicates builtin list function
Fixed a bug where DeleteDuplicates crashed when given an empty list as argument.
Removed non-instructive tests from the automatic documentation
fixed Split behaviour when given an empty list as argument
Changed DeleteDuplicates documentation to confrom to the convention
Replace comparisons with Symbol('True') by expr.is_true(), thus avoiding the overhead of creating an extra Symbol
Merge pull request #136 from proxy-sander/master

Added DeleteDuplicates builtin list function