Adding ziplistDeleteRangeFromOffset

Added `ziplistDeleteRangeFromOffset` allowing to remove more than one entry from ziplist starting from a given entry in the ziplist.
Changed ziplistDelete to return result from ziplistDeleteRangeFromOffset call. In addition, replaced every ziplistDelete double-call to a single ziplistDeleteRangeFromOffset call.

These changes were made due to a "TODO" request in the code.

Tests - I have run `make test` to approve that my changes haven't caused new problems.