Replace all usage of incr/decr with asc/desc as removed in 3.5.0

[krlawrence]

The previously deprecated Order.incr and Order.decr were completely removed in TinkerPop 3.5.0. The manuscript needs to be updated to favor Order.asc and Order.desc and the note about the deprecation needs to be updated. As part of this change an introductory paragraph about TinkerPop 3.5.0 needs to be added.

Several files in the sample-code folder will also need updating.